Base station apparatus and resource allocation method

ABSTRACT

A wireless communication terminal apparatus wherein even when a SC-FDMA signal is divided into a plurality of clusters and the plurality of clusters are then mapped to respective discontinuous frequency bands (when C-SC-FDMA is used), the improvement effect of system throughput can be maintained, while the user throughput can be improved. In the apparatus, a DFT unit ( 210 ) subjects a symbol sequence of time domain to a DFT process, thereby generating signals of frequency domain. A setting unit ( 211 ) divides the signals input from the DFT unit ( 210 ) into a plurality of clusters according to a cluster pattern that is in accordance with an MCS set, an encoding size, or the number of Ranks occurring during MIMO transmissions, which is indicated in those signals input, and then maps the plurality of clusters to the respective ones of a plurality of discontinuous frequency resources, thereby setting a constellation of the plurality of clusters in the frequency domain.

TECHNICAL FIELD

The present invention relates to a radio communication terminalapparatus, a radio communication base station apparatus and a clusterarrangement setting method.

BACKGROUND ART

In 3GPP LTE (3rd Generation Partnership Project Long Term Evolution),studies are being actively carried out on the standardization of mobilecommunication standards in order to realize low-delay and high-speedtransmission.

To realize low-delay and high-speed transmission, OFDM (OrthogonalFrequency Division Multiplexing) is adopted as a downlink (DL) multipleaccess scheme, while SC-FDMA (Single-Carrier Frequency Division MultipleAccess) using DFT (Discrete Fourier Transform) precoding is adopted asan uplink (UL) multiple access scheme. SC-FDMA using DFT precoding formsan SC-FDMA signal (spectrum) by spreading and code-multiplexing a symbolsequence using a DFT matrix (precoding matrix or DFT sequence).

Furthermore, standardization of LTE-Advanced (or IMT (InternationalMobile Telecommunication)-Advanced) that realizes still higher speedcommunication than LTE has been started. LTE-Advanced is expected tointroduce a radio communication base station apparatus (hereinafterreferred to as “base station”) and a radio communication terminalapparatus (hereinafter referred to as “terminal”) capable ofcommunicating at wideband frequencies to realize higher speedcommunication.

In order to maintain single carrier characteristics (e.g. low PAPR(Peak-to-Average Power Ratio) characteristics) of a transmission signalfor realizing high coverage on an LTE uplink, allocation of frequencyresources on the uplink is limited to allocation whereby an SC-FDMAsignal is mapped in a localized manner to continuous frequency bands.

However, when allocation of frequency resources is limited as describedabove, vacant resources are produced in uplink shared frequencyresources (e.g. PUSCH (Physical Uplink Shared CHannel)) and theefficiency of use of frequency resources in the system banddeteriorates, resulting in deterioration of system throughput. Thus,clustered SC-FDMA (C-SC-FDMA) is proposed as a prior art for improvingsystem throughput whereby an SC-FDMA signal is divided into a pluralityof clusters and the plurality of clusters are mapped to discontinuousfrequency resources (e.g. see Non-Patent Literature 1).

According to C-SC-FDMA, a base station compares the states ofavailability of frequency resources (subcarriers or resources blocks(RB)) of a plurality of uplinks or channel quality information (e.g.CQI: Channel Quality Indicator) between a plurality of terminals and thebase station. The base station divides an SC-FDMA signal (spectrum) ofeach terminal by an arbitrary bandwidth according to the level of CQIbetween each terminal and the base station and thereby generates aplurality of clusters. The base station then allocates the plurality ofclusters generated to frequency resources of a plurality of uplinks andreports information indicating the allocation results to the terminals.The terminal divides the SC-FDMA signal (spectrum) by an arbitrarybandwidth, maps the plurality of clusters to the frequency resources ofthe plurality of uplinks allocated by the base station and therebygenerates a C-SC-FDMA signal. The base station applies frequency domainequalization (FDE) processing to the received C-SC-FDMA signal (aplurality of clusters) and combines the plurality of clusters after theequalization processing. The base station then applies IDFT (InverseDiscrete Fourier Transform) processing to the combined signal to obtaina time domain signal.

C-SC-FDMA maps a plurality of clusters to a plurality of discontinuousfrequency resources, and can thereby perform frequency resourceallocation among a plurality of terminals more flexibly than SC-FDMA.Thus, C-SC-FDMA can improve the multiuser diversity effect and canimprove the system throughput in consequence (e.g. see Non-PatentLiterature 2).

CITATION LIST Non-Patent Literature

-   NPL 1-   R1-081842, “LTE-A Proposals for evolution,” 3GPP RAN WG1 #53, Kansas    City, Mo., USA, May 5-9, 2008-   NPL 2-   R1-083011, “Uplink Access Scheme for LTE-Advanced in BW=<20 MHz,”    3GPP RAN WG1 #54, Jeju, Korea, Aug. 18-22, 2008

SUMMARY OF INVENTION Technical Problem

To realize higher speed communication than LTE, it is necessary toimprove not only system throughput but also user throughput per terminalon an LTE-Advanced uplink more than user throughput per terminal on anLTE uplink.

However, an uplink wide radio frequency band (wideband radio channel)has frequency selectivity, and this reduces the frequency correlationbetween channels through which a plurality of clusters which are mappedto different discontinuous frequency bands propagate. Thus, even whenthe base station equalizes a C-SC-FDMA signal (a plurality of clusters)through equalization processing, the equalized channel gain per aplurality of clusters (that is, the frequency channel gain multiplied byan FDE weight) may possibly differ significantly. Thus, the equalizedchannel gain may drastically change at combining points of the pluralityof clusters (that is, division points at which the terminal divides theSC-FDMA signal). That is, discontinuous points are produced in afluctuation of the equalized channel gain at the combining points of theplurality of clusters (that is, envelope of reception spectrum).

Here, maintaining the loss of orthogonality of the DFT matrix minimal inall frequency bands (that is, the sum of frequency bands to which theplurality of clusters are mapped) to which the C-SC-FDMA signal ismapped requires the fluctuation of the equalized channel gain to bemoderate in all frequency bands to which the plurality of clusters aremapped. Therefore, as descried above, when discontinuous points areproduced in the fluctuation of the equalized channel gain at thecombining points of the plurality of clusters, the loss of orthogonalityof the DFT matrix increases in frequency bands to which the C-SC-FDMAsignal is mapped. Thus, the C-SC-FDMA signal is more susceptible to theinfluence of interference between codes (Inter-Symbol Interference: ISI)caused by the loss of orthogonality of the DFT matrix. Furthermore, asthe number of clusters (the number of divisions of the SC-FDMA signal)increases, the number of combining points of the plurality of clusters(discontinuous points) increases, and therefore ISI caused by the lossof orthogonality of the DFT matrix increases. That is, as the number ofclusters (the number of divisions of the SC-FDMA signal) increases,transmission characteristics deteriorate more significantly.

Furthermore, an MCS (Modulation and channel Coding Scheme) set (codingrate and modulation level) corresponding to channel quality of theuplink of each terminal or transmission parameters such as coding sizeare set in the SC-FDMA signal transmitted by each terminal. However, therobustness against ISI caused by the loss of orthogonality of the DFTmatrix (reception sensitivity), that is, the magnitude of allowable ISIdiffers from one transmission parameter to another set in the SC-FDMAsignal. For example, when attention is focused on a modulation levelindicated in the MCS set as a transmission parameter, a modulationscheme of a higher modulation level such as the modulation scheme of 64QAM having a very small Euclidean distance between signal points is moresusceptible to the influence of ISI. That is, even when ISI of the samemagnitude occurs, whether the ISI is allowable or not (that is, whetherthe ISI is within a range of allowable ISI or not) differs depending onthe modulation level set in the SC-FDMA signal (that is, transmissionparameter such as MCS set or coding size). In the case where ISI greaterthan the allowable ISI of a transmission parameter (MCS set or codingsize) set in the SC-FDMA signal is produced, transmissioncharacteristics deteriorate and the user throughput of the terminal inwhich the transmission parameter is set deteriorates.

Thus, when the SC-FDMA signal is divided by an arbitrary bandwidth onlyaccording to a CQI between the base station and each terminal as withthe above described prior art and a plurality of clusters are mapped todiscontinuous frequency bands, although the system throughput isimproved, influences of ISI on the transmission characteristics varydepending on the differences in transmission parameters (MCS set orcoding size) set in the SC-FDMA signal and the user throughput is notimproved.

It is therefore an object of the present invention to provide a radiocommunication terminal apparatus, a radio communication base stationapparatus and a cluster arrangement setting method capable of improvinguser throughput while maintaining the effect of improving systemthroughput when an SC-FDMA signal is divided into a plurality ofclusters and the plurality of clusters are mapped to discontinuousfrequency bands, that is, even when C-SC-FDMA is used.

Solution to Problem

A radio communication terminal apparatus of the present invention adoptsa configuration including a transformation section that applies DFTprocessing to a time domain symbol sequence and generates a frequencydomain signal and a setting section that divides the signal into aplurality of clusters in accordance with a cluster pattern correspondingto an MCS set that is set in the signal, a coding size that is set inthe signal or a rank index during MIMO transmission, maps the pluralityof clusters to a plurality of discontinuous frequency resources andthereby determines an arrangement of the plurality of clusters in afrequency domain.

A radio communication base station apparatus of the present inventionadopts a configuration including a control section that determines acluster pattern of a signal from a radio communication terminalapparatus according to an MCS set that is set in the signal, a codingsize that is set in the signal or a rank index during MIMO transmission,and a reporting section that reports the cluster pattern to the radiocommunication terminal apparatus.

A cluster arrangement setting method of the present invention divides afrequency domain signal generated by applying DFT processing to a timedomain symbol sequence into a plurality of clusters in accordance with acluster pattern corresponding to an MCS set that is set in the signal, acoding size that is set in the signal or a rank index during MIMOtransmission, maps the plurality of clusters to a plurality ofdiscontinuous frequency resources and thereby determines an arrangementof the plurality of clusters.

Advantageous Effects of Invention

According to the present invention, even when an SC-FDMA signal isdivided into a plurality of clusters and the plurality of clusters aremapped to discontinuous frequency bands (when C-SC-FDMA is used), it ispossible to improve user throughput while maintaining the effect ofimproving system throughput.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block configuration diagram of a base station according toEmbodiment 1 of the present invention;

FIG. 2 is a block configuration diagram of a terminal according toEmbodiment 1 of the present invention;

FIG. 3A is a diagram illustrating a relationship between the number ofclusters (cluster spacing) and user throughput according to Embodiment 1of the present invention (when SNR is high);

FIG. 3B is a diagram illustrating a relationship between the number ofclusters (cluster spacing) and user throughput according to Embodiment 1of the present invention (when SNR is low);

FIG. 4 is a diagram illustrating an association between a modulationlevel and the number of clusters or cluster size according to Embodiment1 of the present invention;

FIG. 5A is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 1 of the present invention (whenmodulation level is low);

FIG. 5B is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 1 of the present invention (whenmodulation level is high);

FIG. 6A is a diagram illustrating a combined signal according toEmbodiment 1 of the present invention (when modulation level is low);

FIG. 6B is a diagram illustrating a combined signal according toEmbodiment 1 of the present invention (when modulation level is high);

FIG. 7 is a diagram illustrating an association between a modulationlevel and a cluster spacing according to Embodiment 1 of the presentinvention;

FIG. 8A is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 1 of the present invention (whenmodulation level is low);

FIG. 8B is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 1 of the present invention (whenmodulation level is high);

FIG. 9A is a diagram illustrating a combined signal according toEmbodiment 1 of the present invention (when modulation level is low);

FIG. 9B is a diagram illustrating a combined signal according toEmbodiment 1 of the present invention (when modulation level is high);

FIG. 10 is a diagram illustrating an association between a coding sizeand the number of clusters or cluster size according to Embodiment 1 ofthe present invention;

FIG. 11A is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 1 of the present invention (whencoding size is large);

FIG. 11B is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 1 of the present invention (whencoding size is small);

FIG. 12 is a diagram illustrating an association between a coding sizeand a cluster spacing according to Embodiment 1 of the presentinvention;

FIG. 13A is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 1 of the present invention (whencoding size is large);

FIG. 13B is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 1 of the present invention (whencoding size is small);

FIG. 14 is a diagram illustrating an association between a coding rateand the number of clusters or cluster size according to Embodiment 1 ofthe present invention;

FIG. 15 is a diagram illustrating an association between a coding sizeand a cluster spacing according to Embodiment 1 of the presentinvention;

FIG. 16A is a diagram illustrating an association between a modulationlevel and the number of clusters according to a variation of Embodiment1 of the present invention;

FIG. 16B is a diagram illustrating an association between a modulationlevel and the number of clusters according to a variation of Embodiment1 of the present invention;

FIG. 16C is a diagram illustrating an association between a modulationlevel and a cluster size according to a variation of Embodiment 1 of thepresent invention;

FIG. 16D is a diagram illustrating an association between a modulationlevel and a cluster size according to a variation of Embodiment 1 of thepresent invention;

FIG. 16E is a diagram illustrating an association between a modulationlevel and a cluster spacing according to a variation of Embodiment 1 ofthe present invention;

FIG. 17A is a diagram illustrating an association between a coding sizeand the number of clusters according to a variation of Embodiment 1 ofthe present invention;

FIG. 17B is a diagram illustrating an association between a coding sizeand a cluster size according to a variation of Embodiment 1 of thepresent invention;

FIG. 17C is a diagram illustrating an association between a coding sizeand a cluster size according to a variation of Embodiment 1 of thepresent invention;

FIG. 17D is a diagram illustrating an association between a coding sizeand a cluster spacing according to a variation of Embodiment 1 of thepresent invention;

FIG. 18A is a diagram illustrating an association between a coding rateand the number of clusters according to a variation of Embodiment 1 ofthe present invention;

FIG. 18B is a diagram illustrating an association between a coding sizeand a cluster size according to a variation of Embodiment 1 of thepresent invention;

FIG. 18C is a diagram illustrating an association between a coding sizeand a cluster size according to a variation of Embodiment 1 of thepresent invention;

FIG. 18D is a diagram illustrating an association between a coding sizeand a cluster spacing according to a variation of Embodiment 1 of thepresent invention;

FIG. 19A is a diagram illustrating an association between an MCS set andthe number of clusters according to a variation of Embodiment 1 of thepresent invention;

FIG. 19B is a diagram illustrating an association between an MCS set anda cluster size according to a variation of Embodiment 1 of the presentinvention;

FIG. 19C is a diagram illustrating an association between an MCS set anda cluster spacing according to a variation of Embodiment 1 of thepresent invention;

FIG. 20 is a block configuration diagram of a terminal according to avariation of Embodiment 1 of the present invention;

FIG. 21 is a block configuration diagram of a terminal according toEmbodiment 2 of the present invention;

FIG. 22 is a diagram illustrating an association between a rank indexand the number of clusters or cluster size according to Embodiment 2 ofthe present invention;

FIG. 23A is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 2 of the present invention (when therank index is small);

FIG. 23B is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 2 of the present invention (when therank index is large);

FIG. 24 is a diagram illustrating an association between a rank indexand a cluster spacing according to Embodiment 2 of the presentinvention;

FIG. 25A is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 2 of the present invention (when therank index is small);

FIG. 25B is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 2 of the present invention (when therank index is large);

FIG. 26A is a block configuration diagram of a terminal according toEmbodiment 2 of the present invention (when the rank index is 2);

FIG. 26B is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 2 of the present invention (when therank index is 2);

FIG. 27A is a block configuration diagram of the terminal according toEmbodiment 2 of the present invention (when the rank index is 4);

FIG. 27B is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 2 of the present invention (when therank index is 2);

FIG. 28 is a diagram illustrating an association between a transmissionrate (MCS set) and the number of clusters or cluster size according toEmbodiment 2 of the present invention;

FIG. 29 is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 2 of the present invention;

FIG. 30 is a diagram illustrating an association between a transmissionrate (MCS set) and a cluster spacing according to Embodiment 2 of thepresent invention;

FIG. 31 is a diagram illustrating a method of setting a clusterarrangement according to Embodiment 2 of the present invention;

FIG. 32A is a diagram illustrating an association between a rank indexand the number of clusters according to a variation of Embodiment 2 ofthe present invention;

FIG. 32B is a diagram illustrating an association between a rank indexand the number of clusters according to a variation of Embodiment 2 ofthe present invention;

FIG. 32C is a diagram illustrating an association between a rank indexand a cluster size according to a variation of Embodiment 2 of thepresent invention;

FIG. 32D is a diagram illustrating an association between a rank indexand a cluster size according to a variation of Embodiment 2 of thepresent invention; and

FIG. 32E is a diagram illustrating an association between a rank indexand a cluster spacing according to a variation of Embodiment 2 of thepresent invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

Embodiment 1

FIG. 1 shows a configuration of base station 100 according to thepresent embodiment.

In base station 100, radio receiving section 102 receives a C-SC-FDMAsignal transmitted from each terminal via antenna 101 and appliesreception processing such as down-conversion and A/D conversion to theC-SC-FDMA signal. Radio receiving section 102 then outputs the C-SC-FDMAsignal subjected to the reception processing to CP (Cyclic Prefix)removing section 103.

CP removing section 103 removes a CP added to the head of the C-SC-FDMAsignal inputted from radio receiving section 102.

FFT (Fast Fourier Transform) section 104 performs FFT to the C-SC-FDMAsignal inputted from CP removing section 103 to transform the signalinto frequency domain C-SC-FDMA signals (subcarrier components). FFTsection 104 then outputs the frequency domain C-SC-FDMA signals(subcarrier components) to demapping section 105. Furthermore, FFTsection 104 outputs the subcarrier components including a pilot signalto measuring section 111.

Demapping section 105 extracts C-SC-FDMA signals corresponding tofrequency resources (subcarriers or RBs) used by the respectiveterminals from the C-SC-FDMA signals inputted from FFT section 104 basedon mapping information inputted from control section 113. Demappingsection 105 then outputs the extracted C-SC-FDMA signal to FDE section106.

FDE section 106 equalizes the C-SC-FDMA signals inputted from demappingsection 105 using FDE weights calculated based on estimate values offrequency fluctuations in channels between the base station and therespective terminals estimated by an estimation section (not shown). FDEsection 106 then outputs the equalized signal to combining section 107.

Combining section 107 combines a plurality of clusters making up theC-SC-FDMA signals inputted from FDE section 106 in a frequency domainbased on the number of clusters (a plurality of clusters obtained bydividing the C-SC-FDMA signal), bandwidth per cluster (hereinafterreferred to as “cluster size”) and frequency spacing between clustersinputted from control section 113. Combining section 107 then outputsthe combined C-SC-FDMA signal to IDFT section 108.

IDFT section 108 generates a time domain signal by applying IDFTprocessing to the C-SC-FDMA signals inputted from combining section 107.IDFT section 108 then outputs the generated time domain signal todemodulation section 109.

Demodulation section 109 demodulates the signal inputted from IDFTsection 108 based on MCS information (modulation level) inputted fromscheduler 112 and outputs the demodulated signal to decoding section110.

Decoding section 110 decodes the signal inputted from demodulationsection 109 based on the MCS information (coding rate) and coding sizeinputted from scheduler 112 and outputs the decoded signal as a receivedbit sequence.

On the other hand, measuring section 111 measures an SINR(Signal-to-Interference plus Noise power Ratio) per frequency band(subcarrier) between each terminal and the base station using a pilotsignal (pilot signal transmitted from each terminal) included insubcarrier components inputted from FFT section 104 and therebygenerates channel quality information (e.g. CQI) of each terminal.Measuring section 111 then outputs a CQI of each terminal to scheduler112.

Scheduler 112 receives as input, an MCS set (modulation level(modulation scheme) and coding rate) set in the signal of each terminal,coding size (code block size) set in the signal of each terminal and DFTsize (the number of DFT points) used in DFT section 210 (FIG. 2) ofterminal 200 which will be described later. First, scheduler 112calculates priority in allocation of uplink frequency resources (PUSCH)corresponding to each terminal. Scheduler 112 schedules allocation ofuplink frequency resources (PUSCH) of each terminal using priority ofeach terminal and a CQI of each terminal inputted from measuring section111.

To be more specific, scheduler 112 determines a cluster pattern of thesignal (C-SC-FDMA signal) from each terminal according to an MCS set(modulation level and coding rate) set in the signal (C-SC-FDMA signal)from each terminal or coding size set in the signal (C-SC-FDMA signal)from each terminal. Here, the cluster pattern is represented by thenumber of clusters, cluster size or cluster spacing. That is, scheduler112 functions as a determining section that determines a cluster pattern(the number of clusters, cluster size or cluster spacing) according tothe MCS set or coding size.

Scheduler 112 then outputs frequency resource information indicating theresult of allocation of uplink frequency resources of each terminal(that is, the scheduling result of frequency resource allocation basedon the determined cluster spacing) and spectrum division informationindicating the number of clusters and cluster size of clusters making upthe C-SC-FDMA signal transmitted by each terminal to control section 113and generation section 114. This causes a cluster pattern indicating thenumber of clusters, cluster size or cluster spacing to be reported toeach terminal. Furthermore, scheduler 112 outputs control informationincluding MCS information indicating the MCS set (modulation scheme andcoding rate) set in each terminal and the coding size set in eachterminal to demodulation section 109, decoding section 110 andgeneration section 114.

Control section 113 calculates the number of clusters, cluster size andcluster spacing based on the spectrum division information and frequencyresource information inputted from scheduler 112. Furthermore, controlsection 113 calculates frequency resources to which the C-SC-FDMA signal(a plurality of clusters) of each terminal is mapped based on thecalculated number of clusters, cluster size and cluster spacing. Controlsection 113 then inputs the calculated number of clusters, cluster sizeand cluster spacing to combining section 107 and outputs mappinginformation indicating the frequency resources to which the C-SC-FDMAsignal (a plurality of clusters) of each terminal is mapped to demappingsection 105.

Generation section 114 generates a control signal by converting thespectrum division information, frequency resource information andcontrol information inputted from scheduler 112 to a binary control bitsequence to be reported to each terminal. Generation section 114 outputsthe control signal generated to coding section 115.

Coding section 115 encodes the control signal inputted from generationsection 114 and outputs the encoded control signal to modulation section116.

Modulation section 116 modulates the control signal inputted from codingsection 115 and outputs the modulated control signal to radiotransmitting section 117.

Radio transmitting section 117 applies transmission processing such asD/A conversion, amplification and up-conversion to the control signalinputted from modulation section 116 and transmits the signal subjectedto the transmission processing to each terminal via antenna 101.

Next, FIG. 2 shows a configuration of terminal 200 according to thepresent embodiment.

In terminal 200, radio receiving section 202 receives a control signaltransmitted from base station 100 (FIG. 1) via antenna 201 and appliesreception processing such as down-conversion and A/D conversion to thecontrol signal. Radio receiving section 202 then outputs the controlsignal subjected to the reception processing to demodulation section203. This control signal includes spectrum division informationindicating the number of divisions of a signal transmitted by eachterminal (that is, the number of clusters) and cluster size, frequencyresource information indicating uplink frequency resources allocated toeach terminal and control information indicating MCS information andcoding size or the like.

Demodulation section 203 demodulates the control signal and outputs thedemodulated control signal to decoding section 204.

Decoding section 204 decodes the control signal and outputs the decodedcontrol signal to extraction section 205.

Extraction section 205 extracts the spectrum division information andfrequency resource information directed to the terminal included in thecontrol signal inputted from decoding section 204 and outputs theextracted spectrum division information and frequency resourceinformation to control section 206. Furthermore, extraction section 205outputs the MCS information directed to the terminal and coding sizeindicated in the control information included in the control signalinputted from decoding section 204 to coding section 207 and modulationsection 208.

Control section 206 calculates the number of clusters of an C-SC-FDMAsignal generated by dividing the SC-FDMA signal (that is, output of DFTsection 210) and cluster size based on the spectrum division informationand frequency resource information inputted from extraction section 205.Furthermore, control section 206 calculates frequency resources to whichthe C-SC-FDMA signal (a plurality of clusters) is mapped based onfrequency resource information and the calculated number of clusters andcluster size, and thereby identifies the cluster spacing of clustersmaking up the C-SC-FDMA signal. That is, control section 206 calculatesthe cluster pattern (the number of clusters, cluster size and clusterspacing) reported from base station 100. Control section 206 thenoutputs the calculated cluster pattern to setting section 211. To bemore specific, control section 206 outputs the calculated number ofclusters and cluster size to division section 212 of setting section 211and outputs mapping information indicating frequency resources to whichthe C-SC-FDMA signal (a plurality of clusters) of the terminal is mapped(that is, information indicating the cluster spacing) to mapping section213 of setting section 211.

When the SC-FDMA signal (spectrum) is divided into a plurality ofclusters, suppose it is predetermined between the base station and theterminal that the SC-FDMA signal (spectrum) will be divided in orderfrom a lower frequency part of the spectrum (from a lower output numberof DFT section 210) or from a higher frequency part of the spectrum(from a higher output number of DFT section 210). For example, of aplurality of clusters generated through the division, control section206 calculates frequency resources to which the clusters are mapped inorder from a cluster of a lower frequency (cluster of a lower outputnumber of DFT section 210) or from a cluster of a higher frequency(cluster of a higher output number of DFT section 210).

Coding section 207 encodes a transmission bit sequence based on the MCSinformation (coding rate) and coding size inputted from extractionsection 205 and outputs the encoded transmission bit sequence tomodulation section 208.

Modulation section 208 generates a symbol sequence by modulating thetransmission bit sequence inputted from coding section 207 based on theMCS information (modulation level) inputted from extraction section 205and outputs the generated symbol sequence to multiplexing section 209.

Multiplexing section 209 multiplexes a pilot signal and the symbolsequence inputted from modulation section 208. Multiplexing section 209outputs the symbol sequence with which a pilot signal is multiplexed toDFT section 210. For example, a CAZAC (Constant Amplitude Zero AutoCorrelation) sequence may also be used as the pilot signal. Furthermore,FIG. 2 shows a configuration in which a pilot signal and a symbolsequence are multiplexed before DFT processing, but a configuration mayalso be adopted in which a pilot signal is multiplexed with a symbolsequence after the DFT processing.

DFT section 210 applies DFT processing to the time domain symbolsequence inputted from multiplexing section 209 and generates afrequency domain signal (SC-FDMA signal). DFT section 210 then outputsthe SC-FDMA signal (spectrum) generated to division section 212 ofsetting section 211.

Setting section 211 is provided with division section 212 and mappingsection 213. Setting section 211 divides the SC-FDMA signal (spectrum)inputted from DFT section 210 into a plurality of clusters in accordancewith a cluster pattern inputted from control section 206, maps theplurality of clusters to discontinuous frequency resources respectivelyand thereby determines an arrangement of the C-SC-FDMA signal (aplurality of clusters) in the frequency domain. Setting section 211outputs the C-SC-FDMA signal (a plurality of clusters) generated to IFFT(Inverse Fast Fourier Transform) section 214. Hereinafter, an internalconfiguration of setting section 211 will be described.

Division section 212 of setting section 211 divides the SC-FDMA signal(spectrum) inputted from DFT section 210 into a plurality of clustersaccording to the number of clusters and cluster size indicated in thecluster information inputted from control section 206. Division section212 then outputs the C-SC-FDMA signal made up of the plurality ofclusters generated to mapping section 213.

Mapping section 213 of setting section 211 maps the C-SC-FDMA signal (aplurality of clusters) inputted from division section 212 to frequencyresources (subcarriers or RBs) based on mapping information (informationindicating the cluster spacing) inputted from control section 206.Mapping section 213 then outputs the C-SC-FDMA signal mapped to thefrequency resources to IFFT section 214.

IFFT section 214 performs IFFT on the plurality of frequency bands(subcarriers) to which the C-SC-FDMA signal inputted from mappingsection 213 is mapped and generates a time domain C-SC-FDMA signal.Here, IFFT section 214 inserts Os into frequency bands (subcarriers)other than the plurality of frequency bands (subcarriers) to which theC-SC-FDMA signal (a plurality of clusters) is mapped. IFFT section 214then outputs the time domain C-SC-FDMA signal to CP insertion section215.

CP insertion section 215 adds the same signal as the rear portion of theC-SC-FDMA signal inputted from IFFT section 214 to the head of theC-SC-FDMA signal as a CP.

Radio transmitting section 216 applies transmission processing such asD/A conversion, amplification and up-conversion to the C-SC-FDMA signaland transmits the signal subjected to the transmission processing tobase station 100 (FIG. 1) via antenna 201.

Next, details of cluster pattern determining processing by base station100 and cluster arrangement setting processing (that is, divisionprocessing of the SC-FDMA signal (spectrum) and mapping processing onthe plurality of clusters) by terminal 200 will be described.

A cluster pattern that maximizes user throughput differs from onetransmission parameter to another. As an example of transmissionparameter, a case will be described using FIG. 3A and FIG. 3B where themodulation level (QPSK, 16 QAM, 64 QAM) is used. FIG. 3A (when SNR(Signal-to-Noise power Ratio) is high) and FIG. 3B (when SNR(Signal-to-Noise power Ratio) is low) illustrate a relationship betweena cluster pattern of a C-SC-FDMA signal (here, the number of clusters orcluster spacing) and user throughput. As shown in FIG. 3A and FIG. 3B,the cluster pattern that maximizes user throughput (here, the number ofclusters or cluster spacing) differs from one modulation level toanother. Here, that the cluster pattern that maximizes user throughputdiffers from one modulation level to another may be attributable to thedifference in robustness against ISI among different modulation levels(allowable ISI). That is, base station 100 and terminal 200 can improvethe user throughput by setting an arrangement of the C-SC-FDMA signal (aplurality of clusters) in the frequency domain based on a clusterpattern with allowable ISI among different transmission parameters takeninto consideration. A case has been described in FIG. 3A and FIG. 3Bwhere the modulation level is taken as an example, but the same appliesto other transmission parameters (coding size and coding rate).

Thus, scheduler 112 of base station 100 determines a cluster pattern ofthe C-SC-FDMA signal according to the transmission parameter (MCS set orcoding size) set in the C-SC-FDMA signal from terminal 200. Furthermore,setting section 211 of terminal 200 sets the arrangement of theC-SC-FDMA signal (a plurality of clusters) in the frequency domainaccording to the cluster pattern corresponding to the transmissionparameter (MCS set or coding size) set in the C-SC-FDMA signaltransmitted by the terminal. Hereinafter, methods of setting a clusterarrangement 1-1 to 1-6 will be described.

<Setting Method 1-1>

According to the present setting method, setting section 211 divides anSC-FDMA signal by the number of clusters (the number of divisions)corresponding to the modulation level (modulation scheme) indicated inan MCS set that is set in the C-SC-FDMA signal.

As the modulation level increases, the Euclidean distance between signalpoints becomes shorter and susceptibility to the influence of ISIincreases. That is, the higher the modulation level, the lower is therobustness against ISI (allowable ISI). Thus, setting section 211preferably sets the arrangement of the C-SC-FDMA signal (a plurality ofclusters) in the frequency domain so that ISI decreases as themodulation level set in the C-SC-FDMA signal transmitted by the terminalincreases (as the robustness against ISI decreases).

Here, as the number of clusters of a C-SC-FDMA signal (the number ofdivisions of an SC-FDMA signal) increases, the number of discontinuouspoints in a fluctuation of the equalized channel gain at combiningpoints of a plurality of clusters increases, and therefore ISIincreases. Thus, ISI increases as the number of clusters of theC-SC-FDMA signal increases

In other words, ISI decreases as the number of clusters of the C-SC-FDMAsignal decreases.

Thus, according to the present setting method, setting section 211divides a signal (SC-FDMA signal) in accordance with a cluster patternwith a smaller number of clusters (the number of clusters per certainunit bandwidth) for a higher modulation level indicated in the MCS setthat is set in the signal transmitted by the terminal. That is,scheduler 112 determines a cluster pattern indicating a smaller numberof clusters as the modulation level indicated in the MCS set that is setin the signal transmitted by terminal 200 increases.

Among SC-FDMA signals having the same bandwidth (certain unitbandwidth), the smaller (greater) the number of clusters obtainedthrough division, the wider (narrower) is the bandwidth per cluster,that is, the cluster size per cluster. That is, among SC-FDMA signalshaving the same bandwidth, reducing (increasing) the number of clustersobtained by dividing the SC-FDMA signal is equivalent to widening(narrowing) the cluster size per a plurality of clusters obtained bydividing the SC-FDMA signal. Thus, setting section 211 may also dividethe signal (SC-FDMA signal) in accordance with a cluster pattern with awider cluster size for a higher modulation level indicated in the MCSset that is set in the signal transmitted by the terminal. That is,scheduler 112 may determine a cluster pattern indicating a wider clustersize for a higher modulation level indicated in the MCS set that is setin the signal transmitted by terminal 200.

This will be described more specifically below. Here, as shown in FIG.4, cases using, as a modulation scheme, QPSK (modulation level: low)where two bits are transmitted with one symbol, 16 QAM (modulationlevel: medium) where four bits are transmitted with one symbol, and 64QAM (modulation level: high) where six bits are transmitted with onesymbol will be described. Furthermore, the bandwidth of the C-SC-FDMAsignal in FIG. 5A and FIG. 5B, that is, the total cluster size ofclusters #0 to #3 shown in FIG. 5A is equal to the total cluster size ofclusters #0 and #1 shown in FIG. 5B.

Scheduler 112 of base station 100 decreases the number of clusters(widens the cluster size) as the modulation level increases. To be morespecific, as shown in FIG. 4, scheduler 112 increases the number ofclusters (narrows the cluster size) for QPSK of a low modulation level.On the other hand, as shown in FIG. 4, scheduler 112 decreases thenumber of clusters (widens the cluster size) for 64 QAM of a highmodulation level. That is, scheduler 112 determines a cluster patternthat matches the number of clusters (high, medium, low) or cluster size(narrow, medium, wide) in accordance with the modulation level (low,medium, high). Base station 100 then reports spectrum divisioninformation including the determined cluster pattern (the number ofclusters or cluster size) and frequency resource information to terminal200.

Division section 212 of setting section 211 of terminal 200 divides theSC-FDMA signal (spectrum) inputted from DFT section 210 into a pluralityof clusters according to the cluster pattern determined by scheduler 112(the number of clusters or cluster size). That is, division section 212divides the SC-FDMA signal in accordance with a cluster pattern with asmaller number of clusters (or the wider cluster size) for a highermodulation level indicated in the MCS set that is set in a signaltransmitted by the terminal. Mapping section 213 of setting section 211then maps the plurality of clusters to discontinuous frequency resourcesbased on frequency resource information.

When, for example, the modulation scheme is QPSK (modulation level:low), scheduler 112 determines a cluster pattern (the number of clustersor cluster size) so that the number of clusters increases as shown inFIG. 5A (four clusters #0 to #3 in FIG. 5A), that is, the cluster sizeper cluster becomes narrower. As shown in FIG. 5A, division section 212divides the SC-FDMA signal (spectrum) into four clusters of clusters #0to #3 and mapping section 213 maps four clusters #0 to #3 todiscontinuous frequency resources. As shown in FIG. 5A, a C-SC-FDMAsignal with a high number of clusters (narrow cluster size) is thusgenerated.

On the other hand, when the modulation scheme is 64 QAM (modulationlevel: high), scheduler 112 determines a cluster pattern (the number ofclusters or cluster size) as shown in FIG. 5B so that the number ofclusters decreases (two clusters #0 and #1 in FIG. 5B), that is, thecluster size becomes wider. As shown in FIG. 5B, division section 212divides the SC-FDMA signal (spectrum) into two clusters of cluster #0and cluster #1 and mapping section 213 maps cluster #0 and cluster #1 todiscontinuous frequency resources. Thus, as shown in FIG. 5B, aC-SC-FDMA signal with a low number of clusters (wide cluster size) isgenerated.

Terminal 200 then transmits the C-SC-FDMA signal shown in FIG. 5A(modulation scheme: QPSK) or FIG. 5B (modulation scheme: 64 QAM) to basestation 100 and base station 100 applies equalization processing to thereceived C-SC-FDMA signal and combines the C-SC-FDMA signal (a pluralityof clusters) after the equalization processing. This allows base station100 to obtain a signal after the cluster combination as shown in FIG. 6A(modulation scheme: QPSK) or FIG. 6B (modulation scheme: 64 QAM).

As shown in FIG. 6A, when the modulation level is low (modulationscheme: QPSK), the number of discontinuous points in a fluctuation ofthe equalized channel gain in the combined signal is 3. On the otherhand, as shown in FIG. 6B, when the modulation level is high (modulationscheme: 64 QAM), the number of discontinuous points in a fluctuation ofthe equalized channel gain in the combined signal is 1. That is, asshown in FIG. 6A and FIG. 6B, as the modulation level increases, thenumber of discontinuous points in a fluctuation of the equalized channelgain in the combined signal decreases. That is, the higher themodulation level, the less is ISI generated at combining points(discontinuous points) of a plurality of clusters.

Thus, when the modulation level is high, that is, when the Euclideandistance between signal points is short and robustness against ISI(allowable ISI) is low, the number of clusters of the C-SC-FDMA signalis reduced (or the cluster size is widened). This lessens ISI againstthe C-SC-FDMA signal.

On the other hand, when the modulation level is low, that is, when theEuclidean distance between signal points is long and robustness againstISI (allowable ISI) is great, the number of clusters of C-SC-FDMA signalis increased (the cluster size is narrowed). This causes more clustersto be mapped to a plurality of frequency resources having differentchannel fluctuations, and can thereby improve the frequency diversityeffect. However, as shown in FIG. 6A, when the modulation level islower, the number of discontinuous points in a fluctuation of theequalized channel gain in the combined signal increases (that is, ISIincreases). However, since the robustness against ISI (allowable ISI)becomes greater as the modulation level decreases, the influence of ISIon transmission characteristics is less.

Thus, according to the present setting method, the terminal divides theSC-FDMA signal by the number of clusters (or cluster size) according tothe modulation level indicated in the MCS set. Thus, for a highermodulation level (lower allowable ISI), the terminal reduces the numberof clusters of the C-SC-FDMA signal (reduces the number of combiningpoints (discontinuous points) of clusters), and can thereby reduce ISI.Furthermore, for a lower modulation level (greater allowable ISI), theterminal increases the number of clusters of the C-SC-FDMA signal, andcan thereby improve the frequency diversity effect. Thus, the presentsetting method can improve transmission characteristics according to themodulation level, and can thereby improve user throughput for eachterminal while maintaining the effect of improving system throughput byC-SC-FDMA (by clustering an SC-FDMA signal) no matter what themodulation level is.

Furthermore, the present setting method determines the number ofclusters (cluster size) according to the modulation level, and canthereby control ISI. Thus, when, for example, adaptivemodulation/channel coding (Adaptive Modulation and channel Coding: AMC)control is used, the base station determines the number of clusters(cluster size) according to the modulation level, controls ISI, and canthereby estimate instantaneous ISI beforehand. Thus, the base station ismore likely to be able to select an accurate MCS set in accordance withinstantaneous receiving quality (e.g. instantaneous SINR) with theinfluence of instantaneous ISI taken into account. Thus, the presentsetting method selects an accurate MCS set, and can thereby reduce thenumber of retransmissions due to transmission errors, and can therebyfurther improve user throughput.

<Setting Method 1-2>

Although a case has been described in setting method 1 whereby settingsection 211 divides the SC-FDMA signal by the number of clusterscorresponding to the modulation level indicated in the MCS set that isset in the C-SC-FDMA signal, according to the present setting method,setting section 211 maps a plurality of clusters to frequency resourcesat a cluster spacing corresponding to the modulation level set in theC-SC-FDMA signal.

The wider the cluster spacing of the C-SC-FDMA signal, the lower is thefrequency correlation between channels through which each clusterpropagates. Thus, when base station 100 applies equalization processingbased on a minimum mean square error (MMSE) approach or the like wherebya reception spectrum received after propagating through a frequencyselective channel is not completely reconstructed, a difference inequalized channel gain (power difference and amplitude difference, andphase difference when there is a channel estimation error) at combiningpoints (discontinuous points) of a plurality of clusters making up aC-SC-FDMA signal increases and ISI therefore increases. That is, thewider the cluster spacing of the C-SC-FDMA signal, the greater is ISI.In other words, ISI becomes less as the cluster spacing of the C-SC-FDMAsignal becomes narrower.

Thus, according to the present setting method, for a higher modulationlevel indicated in an MCS set that is set in a signal transmitted by theterminal, setting section 211 maps a signal (SC-FDMA signal) to aplurality of discontinuous frequency resources in accordance with acluster pattern with a narrower cluster spacing. That is, scheduler 112determines a cluster pattern indicating a narrower cluster spacing for ahigher modulation level indicated in the MCS set that is set in thesignal transmitted by terminal 200.

Hereinafter, this will be described more specifically. Here, suppose thenumber of clusters is 2 (cluster #0 and cluster #1 shown in FIG. 8A andFIG. 8B). Furthermore, as with setting method 1-1, a case will bedescribed where QPSK (modulation level: low), 16 QAM (modulation level:medium) and 64 QAM (modulation level: high) as shown in FIG. 7 are usedas the modulation scheme. Furthermore, as with setting method 1-1, thebandwidths of the respective C-SC-FDMA signals in FIG. 8A and FIG. 8Bare the same.

Scheduler 112 of base station 100 narrows the cluster spacing for ahigher modulation level. To be more specific, as shown in FIG. 7,scheduler 112 widens the cluster spacing for QPSK of a low modulationlevel. Furthermore, as shown in FIG. 7, scheduler 112 narrows thecluster spacing for 64 QAM of a high modulation level. That is,scheduler 112 determines a cluster pattern that matches the clusterspacing (wide, medium, narrow) according to the modulation level (low,medium, high). Base station 100 reports frequency resource informationincluding spectrum division information (e.g. the number of clusters: 2)and the determined cluster pattern (cluster spacing) to terminal 200.

Division section 212 of setting section 211 of terminal 200 divides theSC-FDMA signal (spectrum) inputted from DFT section 210 into twoclusters according to the spectrum division information (here, thenumber of clusters: 2). Furthermore, mapping section 213 of settingsection 211 maps the two clusters to discontinuous frequency resourcesaccording to the cluster pattern (cluster spacing) determined byscheduler 112. That is, mapping section 213 maps the plurality ofclusters to a plurality of discontinuous frequency resources inaccordance with a cluster pattern with a narrower cluster spacing for ahigher modulation level indicated in the MCS set that is set in thesignal transmitted by the terminal.

When, for example, the modulation scheme is QPSK (modulation level:low), scheduler 112 determines a cluster pattern (cluster spacing) sothat the cluster spacing becomes wider as shown in FIG. 8A. Mappingsection 213 then maps the two clusters of cluster #0 and cluster #1generated by dividing the SC-FDMA signal (spectrum) by division section212 as shown in FIG. 8A to discontinuous frequency resources separatedapart by the frequency spacing shown in the cluster pattern. As shown inFIG. 8A, a C-SC-FDMA signal having a wide frequency spacing betweencluster #0 and cluster #1 is generated.

On the other hand, when the modulation scheme is 64 QAM (modulationlevel: high), scheduler 112 determines a cluster pattern (clusterspacing) so that the cluster spacing becomes narrower as shown in FIG.8B. As shown in FIG. 8B, mapping section 213 then maps two clusters ofcluster #0 and cluster #1 generated by dividing the SC-FDMA signal(spectrum) by division section 212 to discontinuous frequency resourcesseparated away by the frequency spacing shown in the cluster pattern. Asshown in FIG. 8B, a C-SC-FDMA signal having a wide frequency spacingbetween cluster #0 and cluster #1 is thereby generated.

Terminal 200 then transmits the C-SC-FDMA signal shown in FIG. 8A(modulation scheme: QPSK) or FIG. 8B (modulation scheme: 64 QAM) to basestation 100. Thus, base station 100 obtains a signal after the clustercombination as shown in FIG. 9A (modulation scheme: QPSK) or FIG. 9B(modulation scheme: 64 QAM).

When the modulation level is low (modulation scheme: QPSK) as shown inFIG. 9A, the frequency spacing between cluster #0 and cluster #1 is wideand the frequency correlation between clusters is low. Thus, as shown inFIG. 8A, the difference in equalized channel gain is large at thecombining point (discontinuous point) of the clusters. On the otherhand, when the modulation level is high as shown in FIG. 8B (modulationscheme: 64 QAM), the frequency spacing between cluster #0 and cluster #1is narrow and the frequency correlation between the clusters is high.Thus, as shown in FIG. 9B, the difference in equalized channel gain issmall at the combining point (discontinuous point) of the clusters. Thatis, as shown in FIG. 9A and FIG. 9B, the higher the modulation level,the lower is the difference in equalized channel gain at the combiningpoint (discontinuous point) of the clusters. Thus, the higher themodulation level, the less is ISI generated due to discontinuity at thecombining points among a plurality of clusters.

Thus, when the modulation level is higher, that is, robustness againstISI (allowable ISI) is lower, the cluster spacing of the C-SC-FDMAsignal is narrowed. As with setting method 1-1 (when the number ofclusters is reduced), this makes it possible to reduce ISI with theC-SC-FDMA signal.

On the other hand, when the modulation level is lower, that is,robustness against ISI (allowable ISI) is greater, the cluster spacingof the C-SC-FDMA signal is widened. This makes it possible to improvethe frequency diversity effect resulting from mapping a plurality ofclusters to frequency resources separated further from each other.However, when the modulation level is lower, the spacing betweenclusters making up the C-SC-FDMA signal is widened, and therefore, asshown in, FIG. 9A, the difference in equalized channel gain at thecombining point (discontinuous point) of the clusters becomes greater(that is, ISI increases). However, since the lower the modulation level,the greater is robustness against ISI (allowable ISI), the influence ofISI on transmission characteristics is less.

Thus, according to the present setting method, the terminal maps aplurality of clusters to frequency resources at a cluster spacingaccording to the modulation level indicated in the MCS set. Thus, bynarrowing the cluster spacing of the C-SC-FDMA signal (by increasing thechannel frequency correlation among a plurality of clusters) for ahigher modulation level (lower allowable ISI), the terminal can reduceISI. Furthermore, by widening the cluster spacing of the C-SC-FDMAsignal for a low modulation level (greater allowable ISI), the terminalcan improve the frequency diversity effect. Thus, according to thepresent setting method, as with setting method 1-1, it is possible toimprove user throughput at each terminal while maintaining the effect ofimproving system throughput by C-SC-FDMA (that is, by clustering theSC-FDMA signal) no matter what the modulation level is.

Furthermore, the present setting method determines the cluster spacingaccording to the modulation level, and can thereby reduce ISI. Thus, aswith setting method 1-1, when AMC control is used, the base stationdetermines a cluster spacing according to the modulation level andcontrols ISI, and can thereby estimate instantaneous ISI beforehand. Forthis reason, the base station selects an accurate MCS set according toinstantaneous receiving quality (e.g. instantaneous SINR) with theinfluence of instantaneous ISI taken into account, and can therebyreduce the number of retransmissions caused by transmission errors andfurther improve user throughput.

<Setting Method 1-3>

According to the present setting method, setting section 211 divides theSC-FDMA signal by the number of clusters (the number of divisions)according to a coding size (code block size) set in a C-SC-FDMA signal.

Since the greater the coding size, the higher is the coding gain (orerror correcting capacity), robustness against ISI (allowable ISI)increases. In other words, since the smaller the coding size, the loweris the coding gain (or error correcting capacity), robustness againstISI (allowable ISI) becomes smaller.

Furthermore, assuming that the coding rate and modulation level withrespect to a signal are fixed, the smaller the coding size, the narroweris the bandwidth allocated to the signal in the frequency domain, thatis, the number of allocated RBs decreases.

Therefore, setting section 211 preferably sets an arrangement of aC-SC-FDMA signal (a plurality of clusters) in the frequency domain suchthat the smaller the coding size set in the C-SC-FDMA signal transmittedby the terminal (or the smaller the number of allocated RBs), the lessis ISI.

Thus, according to the present setting method, setting section 211divides the signal (SC-FDMA signal) in accordance with a cluster patternwith a smaller number of clusters (the number of clusters per certainunit bandwidth) for a smaller coding size (for a smaller number ofallocated RBs) set in the signal transmitted by the terminal. That is,scheduler 112 determines a cluster pattern indicating a smaller numberof clusters for a smaller coding size set in the signal transmitted byterminal 200. As in the case of allocation method 1-1, setting section211 may also divide the signal (SC-FDMA signal) in accordance with acluster pattern with a wider cluster size for a smaller coding size setin the signal transmitted by the terminal (or for a smaller number ofallocated RBs).

Hereinafter, this will be described more specifically. Here, as shown inFIG. 10, a case will be described where a coding size (large, medium,small) (or the number of allocated RBs (high, medium, low)) is used.Furthermore, in FIG. 11A and FIG. 11B, suppose an MCS set (coding rateand modulation level) set in a C-SC-FDMA signal is fixed.

Scheduler 112 reduces the number of clusters (widens the cluster size)as the coding size decreases (as the number of allocated RBs becomessmaller). To be more specific, as shown in FIG. 10, scheduler 112determines a cluster pattern that matches the number of clusters (high,medium, low) (or cluster size (narrow, medium, wide)) according to thecoding size (large, medium, small) (or the number of allocated RBs(high, medium, low)). Base station 100 then reports spectrum divisioninformation including the determined cluster pattern (the number ofclusters or cluster size) and frequency resource information to terminal200.

When, for example, the coding size is large (the number of allocated RBsis high), scheduler 112 determines a cluster pattern (the number ofclusters or cluster size) as shown in FIG. 11A such that the number ofclusters increases (six clusters #0 to #5 in FIG. 11A), that is, thecluster size per cluster becomes narrower as with setting method 1-1(FIG. 5A). On the other hand, when the coding size is small (when thenumber of allocated RBs is low), scheduler 112 determines the clusterpattern (the number of clusters or cluster size) such that the number ofclusters decreases (two clusters #0 and #1 in FIG. 11B), that is, thecluster size becomes wider as shown in FIG. 11B as with setting method1-1 (FIG. 5B).

Division section 212 of setting section 211 divides an SC-FDMA signal(spectrum) into a plurality of clusters based on the number of clusters(or cluster size) indicated in the cluster pattern shown in FIG. 11A orFIG. 11B. That is, division section 212 divides the signal in accordancewith a cluster pattern with a smaller number of clusters (or widercluster size) for a smaller coding size set in the signal transmitted bythe terminal (for a smaller number of allocated RBs). Mapping section213 maps the plurality of clusters to discontinuous frequency resourcesbased on frequency resource information.

Thus, when the coding size is smaller (when the number of allocated RBsis smaller), that is, when robustness against ISI (allowable ISI) islower, the number of clusters of the C-SC-FDMA signal is reduced (or thecluster size is widened) as with setting method 1-1. This reduces thenumber of discontinuous points of a fluctuation of the equalized channelgain in the combined signal in base station 100, and can thereby reduceISI with the C-SC-FDMA signal.

Furthermore, when the coding size is larger (when the number ofallocated RBs is higher), that is, when robustness against ISI(allowable ISI) is higher, the number of clusters of the C-SC-FDMAsignal is increased (the cluster size is narrowed) as with settingmethod 1-1. This causes the number of discontinuous points of afluctuation of the equalized channel gain to increase in the combinedsignal, but base station 100 performs error correcting decoding with alarge coding size, and can thereby improve the frequency diversityeffect and obtain a greater coding gain while suppressing the influenceof allowable ISI.

Thus, according to the present setting method, even when the terminaldivides the SC-FDMA signal by the number of clusters (the number ofdivisions) according to the coding size (or the number of allocatedRBs), it is possible to improve user throughput at each terminal whilemaintaining the effect of improving system throughput by C-SC-FDMA (thatis, by clustering the SC-FDMA signal) no matter what the coding size isas with setting method 1-1.

<Setting Method 1-4>

According to the present setting method, setting section 211 maps aplurality of clusters making up a C-SC-FDMA signal to frequencyresources with a cluster spacing corresponding to a coding size (thenumber of allocated RBs) set in a C-SC-FDMA signal.

That is, according to the present setting method, setting section 211maps a signal (SC-FDMA signal) to a plurality of discontinuous frequencyresources in accordance with a cluster pattern with a narrower clusterspacing for a smaller coding size (for a smaller number of allocatedRBs) set in a signal transmitted by the terminal. That is, scheduler 112determines a cluster pattern indicating a narrower cluster spacing for asmaller coding size (or for a smaller number of allocated RBs) set inthe signal transmitted by terminal 200.

Hereinafter, this will be described more specifically. Here, suppose thenumber of clusters is 2 (cluster #0 and cluster #1) as with settingmethod 1-2. Furthermore, as with setting method 1-3 (FIG. 10), a casewill be described as shown in FIG. 12 where the coding size (large,medium, small) (or the number of allocated RBs (high, medium, low)) isused. Furthermore, in FIG. 13A and FIG. 13B, suppose the MCS set (codingrate and modulation level) set in a C-SC-FDMA signal is fixed.

Scheduler 112 narrows a cluster spacing for a smaller coding size (for asmaller number of allocated RBs). To be more specific, as shown in FIG.12, scheduler 112 determines a cluster pattern that matches the clusterspacing (wide, medium, narrow) according to the coding size (large,medium, small) (or the number of allocated RBs (high, medium, low)).Base station 100 then reports frequency resource information includingspectrum division information (e.g. the number of clusters: 2) and thedetermined cluster pattern (cluster spacing) to terminal 200.

When, for example, the coding size is large (the number of allocated RBsis high), scheduler 112 determines a cluster pattern (cluster spacing)such that the cluster spacing becomes wider as shown in FIG. 13A as withsetting method 1-2 (FIG. 8A). On the other hand, when the coding size issmall (when the number of allocated RBs is small), scheduler 112determines a cluster pattern (cluster spacing) such that the clusterspacing becomes narrower as shown in FIG. 13B as with setting method 1-2(FIG. 8B).

Division section 212 of setting section 211 then divides an SC-FDMAsignal (spectrum) into two clusters of cluster #0 and cluster #1 asshown in FIG. 13A or FIG. 13B based on spectrum division information(here, the number of clusters: 2). Furthermore, mapping section 213 ofsetting section 211 maps the two clusters of cluster #0 and cluster #1to discontinuous frequency resources based on a cluster spacingindicated in the cluster pattern as shown in FIG. 13A or FIG. 13B. Thatis, mapping section 213 maps the plurality of clusters to a plurality ofdiscontinuous frequency resources in accordance with a cluster patternwith a narrower cluster spacing for a smaller coding size (a smallernumber of allocated RBs) set in a signal transmitted by the terminal.

Thus, when the coding size is smaller (the number of allocated RBs issmaller), that is, when robustness against ISI (allowable ISI) is lower,the cluster spacing of the C-SC-FDMA signal is narrowed as with settingmethod 1-2. Thus, the frequency correlation between clusters (here,between cluster #0 and cluster #1) becomes higher. Since a fluctuationof the equalized channel gain at combining points (discontinuous points)of clusters become moderate (that is, the difference in equalizedchannel gain becomes smaller), ISI with the C-SC-FDMA signal can bereduced.

Furthermore, when the coding size is larger (the number of allocated RBsis higher), that is, robustness against ISI (allowable ISI) is higher,the spacing of clusters making up a C-SC-FDMA signal is widened as withsetting method 1-2. Although this causes the frequency correlationbetween clusters (here, between cluster #0 and cluster #1) to becomelower (fluctuation of the equalized channel gain at combining points(discontinuous points) of clusters becomes drastic), by performing errorcorrecting decoding with a large coding size, it is possible to improvethe frequency diversity effect and thereby obtain a large coding gainwhile suppressing the influence of allowable ISI.

Thus, according to the present setting method, even when the terminalmaps a plurality of clusters to frequency resources with a clusterspacing that matches the coding size (or the number of allocated RBs),it is possible to improve user throughput for each terminal whilemaintaining the effect of improving system throughput by C-SC-FDMA (byclustering an SC-FDMA signal) no matter what the coding size is as withsetting method 1-2.

<Setting Method 1-5>

According to the present setting method, setting section 211 divides anSC-FDMA signal by the number of clusters (the number of divisions)according to a coding rate indicated in an MCS set that is set in aC-SC-FDMA signal.

With data of the same coding size, longer encoded data is generated asthe coding rate decreases. That is, the lower the coding rate, thehigher is the coding gain (or error correcting capacity), and robustnessagainst ISI (allowable ISI) thereby increases. In other words, since thehigher the coding rate, the lower is the coding gain (or errorcorrecting capacity), and robustness against ISI (allowable ISI) therebydecreases.

Thus, according to the present setting method, setting section 211divides a signal (SC-FDMA signal) in accordance with a cluster patternwith a smaller number of clusters (the number of clusters per certainunit bandwidth) for a higher coding rate indicated in an MCS set that isset in the signal transmitted by the terminal. That is, scheduler 112determines a cluster pattern indicating a smaller number of clusters fora higher coding rate indicated in the MCS set that is set in the signaltransmitted by terminal 200. Setting section 211 may also divide asignal (SC-FDMA signal) in accordance with a cluster pattern with awider cluster size for a higher coding rate indicated in the MCS setthat is set in the signal transmitted by the terminal as with allocationmethod 1.

Hereinafter, this will be described more specifically. Here, as shown inFIG. 14, a case will be described where the coding rate (low, medium,high) is used. Furthermore, suppose the coding size and modulation level(modulation scheme) are fixed here.

Scheduler 112 reduces the number of clusters (widens the cluster size)for a higher coding rate. To be more specific, as shown in FIG. 14,scheduler 112 determines a cluster pattern that matches the number ofclusters (high, medium, low) (or cluster size (narrow, medium, wide))according to the coding rate (low, medium, high). Base station 100 thenreports spectrum division information and frequency resource informationincluding the determined cluster pattern (the number of clusters orcluster size) to terminal 200.

When, for example, the coding rate is low, scheduler 112 determines acluster pattern (the number of clusters or cluster size) such that thenumber of clusters increases, that is, the cluster size per clusterbecomes narrower as with setting method 1-3 (FIG. 11A). On the otherhand, when the coding rate is high, scheduler 112 determines a clusterpattern (the number of clusters or cluster size) such that the number ofclusters decreases, that is, the cluster size becomes wider as withsetting method 1-3 (FIG. 11B).

Division section 212 of setting section 211 divides an SC-FDMA signal(spectrum) into a plurality of clusters based on the number of clusters(or cluster size) indicated in the cluster pattern. That is, divisionsection 212 divides the signal in accordance with a cluster pattern witha smaller number of clusters (or a wider cluster size) for a highercoding rate indicated in the MCS set that is set in the signaltransmitted by the terminal. Mapping section 213 of setting section 211then maps a plurality of clusters to discontinuous frequency resourcesbased on frequency resource information.

Thus, by reducing the number of clusters of the C-SC-FDMA signal (orwidening the cluster size) for a higher coding rate, that is, smallerrobustness against ISI (allowable ISI), it is possible to reduce ISIwith the C-SC-FDMA signal as with setting method 1-1.

Furthermore, by increasing the number of clusters of the C-SC-FDMAsignal (narrowing the cluster size) for a lower coding rate, that is,high robustness against ISI (allowable ISI) and by performing errorcorrecting decoding with a low coding rate as with setting method 1-1,it is possible to improve the frequency diversity effect whilesuppressing the influence of allowable ISI.

Thus, according to the present setting method, even when the terminaldivides the SC-FDMA signal by the number of clusters (the number ofdivisions) that matches the coding rate, it is possible to improve userthroughput for each terminal while maintaining the effect of improvingsystem throughput by C-SC-FDMA (by clustering an SC-FDMA signal) nomatter what the coding rate is as with setting method 1-1.

Furthermore, the present setting method determines the number ofclusters (size) according to the coding rate, and can thereby controlISI. Thus, when AMC control is used as with setting method 1-1, the basestation determines the number of clusters (size) according to the codingrate and controls ISI, and can thereby estimate instantaneous ISIbeforehand. For this reason, the base station selects an accurate MCSset corresponding to instantaneous receiving quality (e.g. instantaneousSINR) with the influence of instantaneous ISI taken into account, andcan thereby reduce the number of retransmissions caused by transmissionerrors and further improve user throughput.

<Setting Method 1-6>

According to the present setting method, setting section 211 maps aplurality of clusters making up a C-SC-FDMA signal to frequencyresources with a cluster spacing that matches a coding rate indicated inan MCS set that is set in the C-SC-FDMA signal.

That is, according to the present setting method, setting section 211maps the signal (SC-FDMA signal) to a plurality of discontinuousfrequency resources in accordance with a cluster pattern with a narrowercluster spacing for a higher coding rate indicated in an MCS set that isset in the signal transmitted by the terminal. That is, scheduler 112determines a cluster pattern indicating a narrower cluster spacing for ahigher coding rate indicated in the MCS set that is set in the signaltransmitted by terminal 200.

Hereinafter, this will be described more specifically. Here, suppose thenumber of clusters is 2 as with setting method 1-2. Furthermore, as withsetting method 1-5 (FIG. 14), a case will be described as shown in FIG.15 where the coding rate (low, medium, high) is used. Furthermore,suppose the coding size and modulation level are fixed here.

Scheduler 112 narrows the cluster spacing for a higher coding rate. Tobe more specific, as shown in FIG. 15, scheduler 112 determines acluster pattern with a cluster spacing (wide, medium, narrow) thatmatches the coding rate (low, medium, high). Base station 100 thenreports spectrum division information (e.g. the number of clusters: 2)and frequency resource information including the determined clusterpattern (cluster spacing) to terminal 200.

When, for example, the coding rate is low, scheduler 112 determines acluster pattern (cluster spacing) such that the cluster spacing becomeswider as with setting method 1-4 (FIG. 13A). On the other hand, when thecoding rate is high, scheduler 112 determines a cluster pattern (clusterspacing) so that the cluster spacing becomes narrower as with settingmethod 1-4 (FIG. 13B).

Division section 212 of setting section 211 divides the SC-FDMA signal(spectrum) into a plurality of clusters based on spectrum divisioninformation. Furthermore, mapping section 213 of setting section 211maps the plurality of clusters to discontinuous frequency resourcesbased on a cluster spacing indicated in the cluster pattern. That is,mapping section 213 maps the plurality of clusters to a plurality ofdiscontinuous frequency resources in accordance with a cluster patternwith a narrower cluster spacing for a higher coding rate set in thesignal transmitted by the terminal.

Thus, the cluster spacing of the C-SC-FDMA signal is narrowed for ahigher coding rate, that is, smaller robustness against ISI (allowableISI), and it is thereby possible to reduce ISI with the C-SC-FDMA signalas with setting method 1-2.

Furthermore, by widening the spacing of clusters making up the C-SC-FDMAsignal for a lower coding rate, that is, greater robustness against ISI(allowable ISI) and performing error correcting decoding at a lowercoding rate as with setting method 1-2, it is possible to improve thefrequency diversity effect while suppressing the influence of allowableISI.

Thus, according to the present setting method, even when the terminalmaps a plurality of clusters to frequency resources at a cluster spacingthat matches the coding rate, it is possible to improve user throughputfor each terminal while maintaining the effect of improving systemthroughput by C-SC-FDMA (by clustering an SC-FDMA signal) no matter whatthe coding rate is as with setting method 1-2.

Furthermore, the present setting method determines a cluster spacingaccording to the coding rate, and can thereby control ISI. Thus, as withsetting method 1-2, when AMC control is used, the base stationdetermines a cluster spacing according to the coding rate, controls ISI,and can thereby estimate instantaneous ISI beforehand. Thus, the basestation selects an accurate MCS set corresponding to instantaneousreceiving quality (e.g. instantaneous SINR) with the influence ofinstantaneous ISI taken into account, and can thereby reduce the numberof retransmissions caused by transmission errors and further improveuser throughput.

Methods of setting a cluster arrangement 1-1 to 1-6 have been describedso far.

Thus, according to the present embodiment, the terminal divides theSC-FDMA signal (spectrum) into a plurality of clusters in accordancewith a cluster pattern that matches the MCS set (modulation level,coding rate) or coding size and maps the plurality of clusters todiscontinuous frequency resources. This allows the terminal to set anarrangement of the plurality of clusters in the frequency domainaccording to the difference in robustness against ISI (allowable ISI)per transmission parameter. Thus, according to the present embodiment,when dividing the SC-FDMA signal into a plurality of clusters andmapping the plurality of clusters to discontinuous frequency bands, thatis, even when using C-SC-FDMA, it is possible to improve transmissioncharacteristics for different terminals in which different transmissionparameters are set and improve user throughput while maintaining theeffect of improving system throughput.

In the present embodiment, base station 100 may set a threshold todetermine a cluster pattern. Thus, base station 100 compares atransmission parameter (modulation level, coding rate or coding size)set in each terminal with the threshold, and can thereby determine acluster pattern. Furthermore, each terminal can easily perform divisionprocessing on an SC-FDMA signal (spectrum) and mapping processing on aC-SC-FDMA signal (a plurality of clusters). Hereinafter, an examplewhere base station 100 sets a threshold and determines a cluster patternwill be described using FIG. 16 to FIG. 19. In FIG. 16 to FIG. 19, B_(i)(i=0, 1, . . . ) is a bandwidth (cluster size) per cluster and shows,for example, a minimum bandwidth (minimum cluster size) defined pertransmission parameter in a range separated by a threshold and holds therelationship B_(i)≦B_(i+1). Furthermore, B′_(i) (i=0, 1, . . . ) shows amaximum cluster spacing defined per transmission parameter in a rangeseparated by a threshold and holds the relationship B′_(i)≧B′_(i+1).

For example, base station 100 may set a threshold in the modulationlevel and thereby determine a cluster pattern. For example, as shown inFIG. 16A, base station 100 may set a threshold so as to separate betweena plurality of modulation levels by a certain range of modulation level,compare modulation level (A) set in each terminal with the threshold anddetermine the number of clusters (X). To be more specific, in FIG. 16A,base station 100 determines the number of clusters X to be 4 whenmodulation level (A) is BPSK to QPSK, determines the number of clustersX to be 3 when modulation level (A) is 8 PSK to 16 QAM, determines thenumber of clusters X to be 2 when modulation level (A) is 32QAM to 64QAM and determines the number of clusters X to be 1 when modulationlevel (A) is 128QAM to 256QAM. That is, in FIG. 16A, a fixed number ofclusters is determined for a certain range of modulation level.

Furthermore, as shown in method 1 in FIG. 16B, base station 100 may alsoset a threshold per modulation level and set an upper limit of thenumber of clusters X per modulation level. For example, as shown inmethod 1 in FIG. 16B, base station 100 determines the number of clusterswhose upper limit is the number of clusters X=4 when modulation level(A) is BPSK and determines the number of clusters whose upper limit isthe number of clusters X=2 when modulation level (A) is 16 QAM. The sameapplies to QPSK and 64 QAM as well. This allows setting section 211 ofeach terminal to set the number of clusters so as to prevent ISI greaterthan allowable ISI per modulation level from occurring. Furthermore, asshown in method 2 in FIG. 16B, base station 100 may also set a lowerlimit and upper limit to the number of clusters X per modulation level.For example, as shown in method 2 in FIG. 16B, base station 100determines the number of clusters within a range of 2≦X≦4 whenmodulation level (A) is BPSK and determines the number of clusterswithin a range of 1≦X≦2 when modulation level (A) is 16 QAM. This allowssetting section 211 of each terminal to only set the number of clustersX corresponding to user throughput of a certain value or greaterincluding a maximum value as shown in FIG. 3A or FIG. 3B. Furthermore,base station 100 limits the range of the number of clusters X permodulation level, and can thereby reduce the number of reporting bits toreport the number of clusters X.

Furthermore, as shown in FIG. 16C, base station 100 may set a thresholdso as to separate between a plurality of modulation levels for everycertain range of modulation level and set cluster size (Y) for everyrange of modulation level. According to method 1 in FIG. 16C, as withmethod 1 in FIG. 16B, base station 100 determines one cluster size Ywhose lower limit corresponds to a minimum cluster size (B₀, B₁, B₂, B₃shown in method 1 in FIG. 16C) defined for every range of modulationlevel. As shown in method 1 in FIG. 16C, for BPSK to QPSK which is arange having a minimum modulation level (that is, when allowable ISI ismaximum), base station 100 may determine an arbitrary value for clustersize Y. Furthermore, according to method 2 in FIG. 16C as with method 2in FIG. 16B, an upper limit and a lower limit of cluster size Y are setfor every range of modulation level.

Furthermore, when base station 100 calculates cluster size (Y) using thenumber of clusters (X), as shown in FIG. 16D, base station 100 may set athreshold per modulation level, set the number of clusters X_(a) permodulation level and calculate cluster size Y. Here, X_(a) (a=0, 1, 2, .. . , a is a number assigned for every range of modulation levelseparated by a threshold) represents the number of clusters set forevery range (a) of modulation level. Furthermore, B represents a totalbandwidth used for a C-SC-FDMA signal (that is, the sum of respectivecluster sizes). To be more specific, in FIG. 16D, base station 100 usesthe number of clusters X_(a) set per modulation level (a=0, 1, 2, . . .) to calculate cluster size Y=B/X_(a) set in the modulation level.

Furthermore, as shown in FIG. 16E, base station 100 may also set athreshold so as to separate between a plurality of modulation levels forevery certain range of modulation level and set cluster spacing (Z) forevery range of modulation level. In FIG. 16E, base station 100determines cluster spacing Z whose upper limit is a maximum clusterspacing (B′₀, B′₁, B′₂, B′₃ shown in FIG. 16E) for every range ofmodulation level. As shown in FIG. 16E, for BPSK to QPSK which is arange having a minimum modulation level, base station 100 may set anarbitrary value for cluster spacing Z.

Furthermore, as with FIG. 16A to FIG. 16E, base station 100 may set athreshold for a coding size and determine a cluster pattern. Forexample, as shown in FIG. 17A, base station 100 may set a threshold soas to separate between coding sizes for every certain range of codingsize, compare coding size (N) set in each terminal with the thresholdand determine the number of clusters (X). To be more specific, in FIG.17A, base station 100 determines the number of clusters X to be 1 whencoding size N is 100 bits or less and determines the number of clustersX to be 2 when coding size N is 101 bits or more and 500 bits or less.The same applies to a case where coding size N is 501 bits or more and1000 bits or less and a case where coding size N is 1001 bits or more.

Furthermore, as shown in FIG. 17B, base station 100 may set cluster size(Y) for every range of coding size. According to method 1 in FIG. 17B,as with method 1 in FIG. 16C, base station 100 determines one clustersize Y whose lower limit corresponds to a minimum cluster size (B₀, B₁,B₂, B₃ shown in method 1 in FIG. 17B) defined for every range of codingsize. According to method 1 in FIG. 17B, when coding size N is 1001 bitsor more, base station 100 may determine an arbitrary value for clustersize Y. Furthermore, as shown in method 2 in FIG. 17B, base station 100may set a lower limit and upper limit of cluster size Y for every rangeof coding size as with method 2 in FIG. 16C.

Furthermore, when base station 100 calculates cluster size (Y) using thenumber of clusters (X), as with FIG. 16D, base station 100 may set thenumber of clusters X_(n) for every range of coding size as shown in FIG.17C and calculate cluster size Y. Here, X_(n) (n=0, 1, 2, . . . , n is anumber assigned for every range of coding size separated by a threshold)represents the number of clusters set for every range (n) of codingsize. To be more specific, in FIG. 17C, as with FIG. 16D, using thenumber of clusters X_(n) set for every range of coding size (n=0, 1, 2,. . . ), cluster size Y=B/X_(n) set for the coding size is calculated.As shown in FIG. 17C, in a range in which coding size N is 1001 bits ormore, base station 100 may determine an arbitrary value for cluster sizeY.

Furthermore, as shown in FIG. 17D, base station 100 may set clusterspacing (Z) for every range of coding size. In FIG. 17D, as with FIG.16E, base station 100 determines a cluster spacing whose upper limitcorresponds to a maximum cluster spacing (B′₀, B′₁, B′₃ shown in FIG.17D) for every range of coding size. As shown in FIG. 17D, for a rangein which coding size (N) is 1001 bits or more, base station 100 may setan arbitrary value for cluster spacing (Z).

Furthermore, as with FIG. 16A to FIG. 16E, base station 100 may set athreshold for a coding rate and determine a cluster pattern. Forexample, as shown in FIG. 18A, base station 100 sets a threshold so asto separate between coding rates for every certain range of coding rate,compare coding rate (R) set in each terminal with the threshold anddetermine the number of clusters (X). To be more specific, in FIG. 18A,base station 100 determines the number of clusters X to be 4 when codingrate R is ⅓ or below and determines the number of clusters X to be 3when coding rate R is greater than ⅓ and ½ or below. The same will applyto a case where coding rate R is greater than ½ and ⅔ or below and acase where coding rate R is greater than ⅔.

Furthermore, as shown in FIG. 18B, base station 100 may set cluster size(Y) for every range of coding rate. According to method 1 in FIG. 18B aswith method 1 in FIG. 16C, base station 100 determines one cluster sizeY whose lower limit corresponds to a minimum cluster size (B₀, B₁, B₂,B₃ shown in method 1 in FIG. 18B) defined for every range of codingrate. In FIG. 18B, when coding rate R is ⅓ or below, base station 100may set an arbitrary value for cluster size Y. Furthermore, according tomethod 2 in FIG. 18B, as with method 2 in FIG. 16C, an upper limit and alower limit of cluster size Y are set for every range of coding rate.

When base station 100 calculates cluster size (Y) using the number ofclusters (X), as shown in FIG. 18C, as with FIG. 16D, base station 100may set the number of clusters X_(r) for every range of coding rate andcalculate cluster size (Y). Here, X_(r) (r=0, 1, 2, . . . , r is anumber assigned to each range of coding rate separated by a threshold)represents the number of clusters set for every range (r) of codingrate. To be more specific, in FIG. 18C as with FIG. 16D, cluster sizeY=B/X_(r) set in the coding rate is calculated using the number ofclusters X_(r) set for every range of coding rate (r=0, 1, 2, . . . ).As shown in FIG. 18C, for a range where coding rate R is 100 bits orless, base station 100 may set an arbitrary value for cluster size Y.

Furthermore, as shown in FIG. 18D, base station 100 may also set clusterspacing (Z) for every range of coding rate. In FIG. 18D, as with FIG.16E, base station 100 determines cluster spacing (Z) whose upper limitis a maximum cluster spacing (B′₀, B′₁, B′₂, B′₃ shown in FIG. 18D) forevery range of coding rate. As shown in FIG. 18D, in a range wherecoding rate (R) is ⅓ or below, base station 100 may set an arbitraryvalue for cluster spacing (Z).

Furthermore, a case has been described in the present embodiment wherebase station 100 determines a cluster pattern (the number of clusters,cluster size or cluster spacing) according to the modulation level,coding rate or coding size. However, in the present invention, basestation 100 may also determine a cluster pattern by combining aplurality of transmission parameters (modulation level, coding rate andcoding size). For example, base station 100 may also determine a clusterpattern by combining the modulation level and coding rate, that is,according to an MCS set. When, for example, AMC control is used wherebythe modulation level and coding rate are simultaneously controlled, basestation 100 can simultaneously control robustness against ISI caused byboth the modulation level and coding rate. For example, as shown in FIG.19A, base station 100 may determine the number of clusters (X) for eachMCS set expressed by the modulation level and coding rate, determinecluster size (Y) for each MCS set as shown in FIG. 19B or determinecluster spacing (Z) for each MCS set as shown in FIG. 19C.

Furthermore, although a case has been described in FIG. 16 to FIG. 19where a cluster pattern is determined without taking the SINR (oraverage SNR) into account, the present invention may change theassociations in FIG. 16 to FIG. 19 according to a fluctuation of theSINR (or average SNR).

Furthermore, in the present embodiment when terminal 200 multiplexes aplurality of codewords (coding unit, codeword: CW) in the frequencydomain as shown in FIG. 20 and transmits the codewords to base station100, base station 100 may determine a cluster pattern for each CWtransmitted from terminal 200. Here, when CW #1 to CW #(M−1) aremultiplexed in the frequency domain and transmitted as shown in FIG. 20,terminal 200 divides the CW into a plurality of clusters through thedivision section provided for each CW and frequency-multiplexes clustersper CW through the mapping section.

Furthermore, when different transmission rates are used among aplurality of CWs, terminal 200 may decrease the number of clusters(widen the cluster size) or narrow the cluster spacing for a CW having ahigher transmission rate and thereby set an arrangement of a pluralityof clusters making up the CW in the frequency domain. For a highertransmission rate, robustness against ISI needs to be increased. Thus,it is possible to reduce ISI by increasing the number of clusters(widening the cluster size) for CWs with high transmission rates ornarrowing the cluster spacing, and increase robustness against ISI inconsequence. This makes it possible to further improve transmissioncharacteristics for each CW according to the transmission rate andfurther improve transmission rates of all CWs that is, throughput perterminal (user throughput).

Furthermore, a case has been described in the present embodiment wherebase station 100 determines a cluster pattern (the number of clusters,cluster size or cluster spacing) and reports the cluster pattern toterminal 200. However, in the present invention, base station 100 mayreport only frequency resource information to terminal 200 every timebase station 100 communicates with terminal 200 and terminal 200 maydetermine a cluster pattern (the number of clusters, cluster size orcluster spacing) according to transmission parameters of a signaltransmitted by the terminal.

Furthermore, for example, base station 100 may report frequency resourceinformation indicating a frequency band allocated with the number ofclusters, cluster size and cluster spacing taken into account toterminal 200. To be more specific, base station 100 (scheduler 112 ofbase station 100) may perform scheduling and thereby perform allocationprocessing of allocating a frequency band to terminal 200 showing amaximum SINR in a certain frequency band (subcarrier). Base station 100repeatedly performs the above allocation processing in differentfrequency bands and thereby performs frequency resource allocation of aC-SC-FDMA signal made up of a plurality of clusters. Base station 100then reports frequency resource information indicating the frequencyresource allocation result of the C-SC-FDMA signal of terminal 200 toterminal 200. Base station 100 also performs the above describedfrequency resource allocation processing on terminals other thanterminal 200. This allows base station 100 to schedule allocation offrequency resources for all terminals located in the cell of basestation 100. Furthermore, terminal 200 may map an SC-FDMA signalaccording to the frequency band indicated in the frequency resourceinformation reported from base station 100. Thus, terminal 200 dividesthe SC-FDMA signal into a plurality of clusters in accordance with acluster pattern corresponding to transmission parameters of a signaltransmitted by the terminal and maps the plurality of clusters todiscontinuous frequency resources, and can thereby obtain effectssimilar to those of the present embodiment.

Embodiment 2

The present embodiment will describe a case where MIMO (Multi-InputMulti-Output) transmission which is one of transmission techniques forrealizing high-speed, large-volume data transmission is used. The MIMOtransmission technique can increase throughput by providing a pluralityof antennas for both a base station and a terminal, providing aplurality of propagation paths (streams) in a space between radiotransmission and reception on the same time and the same frequencyresources and spatially multiplexing the respective streams (a pluralityof different data signal sequences are transmitted using a plurality ofstreams).

When a rank index indicating a spatial multiplexing number (or thenumber of signals separated on the receiving side) increases in MIMOtransmission, the number of signal sequences (layers) that can bemultiplexed (parallel transmission) in the space domain increases. Thatis, when the rank index increases, the number of layers in the spacedomain that needs to be separated increases at the base station which isthe receiving side, and therefore ISI from a certain layer to adifferent layer, that is, ISI between layers increases.

Furthermore, when a channel through which each layer propagates hasfrequency selectivity, ISI for each layer is also generated in C-SC-FDMAas described in Embodiment 1.

Therefore, when the rank index increases in a channel having frequencyselectivity, this causes ISI between layers that may affect signalseparation in the space domain to increase. To reduce ISI betweenlayers, the terminal preferably reduces ISI per layer as the rank indexincreases during MIMO transmission as with Embodiment 1. Thus, theterminal according to the present embodiment divides a CW (codeword)which is an SC-FDMA signal into a plurality of clusters in accordancewith a cluster pattern corresponding to the rank index during MIMOtransmission and maps the plurality of clusters to discontinuousfrequency domains.

Hereinafter, this will be described more specifically. FIG. 21 shows aconfiguration of terminal 300 according to the present embodiment.Terminal 300 is provided with M antennas (antennas 201-1 to 201-M) thattransmit CWs (a plurality of clusters) using M streams.

Furthermore, terminal 300 is provided with C-SC-FDMA processing sections301-1 to 301-N corresponding in number to rank index N, made up ofcoding section 207, modulation section 208, multiplexing section 209,DFT section 210 and division section 212. Furthermore, terminal 300 isprovided with transmission processing sections 303-1 to 303-Mcorresponding in number to antennas 201-1 to 201-M, made up of mappingsection 213, IFFT section 214, CP insertion section 215 and radiotransmitting section 216. Thus, terminal 300 is provided with settingsection 211 made up of N division sections 212 and M mapping sections213. Furthermore, N and M satisfy a relationship of N≦M.

C-SC-FDMA processing sections 301-1 to 301-N apply processing similar tothat of coding section 207 to division section 212 of Embodiment 1 totheir respective inputted transmission bit sequences (CW) and therebygenerate C-SC-FDMA signals (a plurality of clusters). C-SC-FDMAprocessing sections 301-1 to 301-N output the C-SC-FDMA signalsgenerated to precoding section 302.

Precoding section 302 receives a precoding matrix (or precoding weight)from control section 206. Here, precoding information indicating theprecoding matrix is reported from a base station (not shown) to terminal300. For example, the precoding information may show a number indicatingeach precoding matrix and control section 206 may calculate eachprecoding matrix based on the number indicated in the precodinginformation.

Precoding section 302 multiplies the C-SC-FDMA signals inputted fromC-SC-FDMA processing sections 301-1 to 301-N by a single precodingmatrix. Precoding section 302 then outputs the precoded C-SC-FDMAsignals to transmission processing sections 303-1 to 303-M stream bystream.

Transmission processing sections 303-1 to 303-M apply processing similarto that of mapping section 213 to radio transmitting section 216 ofEmbodiment 1 to the respectively inputted precoded C-SC-FDMA signals andtransmit the C-SC-FDMA signals after the transmission processing to thebase station via antennas 201-1 to 201-M.

Here, setting section 211 divides an SC-FDMA signal of each layer (here,layer #1 to layer #N) into a plurality of clusters in accordance with acluster pattern inputted from control section 206, that is, a clusterpattern corresponding to an MCS set that is set in a signal transmittedby the terminal, coding size or the rank index during MIMO transmissionand maps the plurality of clusters to discontinuous frequency resources.

On the other hand, a scheduler (not shown) of the base station accordingto the present embodiment determines a cluster pattern of a C-SC-FDMAsignal from each terminal according to an MCS set (modulation level andcoding rate) set in the C-SC-FDMA signal from each terminal, coding sizeor the rank index during MIMO transmission of each terminal. The basestation reports the determined cluster pattern to each terminal.

Next, methods of setting a cluster arrangement 2-1 to 2-6 by settingsection 211 (division sections 212 and mapping sections 213) of terminal300 will be described in detail.

In the following descriptions, the number of antennas (the number ofstreams) is assumed to be 4 and terminal 300 is provided with antennas201-1 to 201-4. Furthermore, suppose the number of CWs simultaneouslytransmitted by terminal 300 is 2. For simplicity of explanation, of thecomponents of terminal 300 shown in FIG. 21, only DFT section 210,setting section 211 (division section 212 and mapping section 213),precoding section 302, IFFT section 214 and antenna 201 are illustratedas shown in FIG. 23A and FIG. 23B, for example. For example, in FIG. 23Aand FIG. 23B, terminal 300 is provided with four mapping sections 213and IFFT sections 214 corresponding in number to the number of antennasof 4 and is also provided with DFT sections 210 and division sections212 corresponding in number to the rank index (e.g. the rank index: 2 inFIG. 23A, the rank index: 4 in FIG. 23B). Here, when the number of CWssimultaneously transmitted by terminal 300 is smaller than the rankindex and the number of CWs is smaller than the number of streams asshown in FIG. 23B, terminal 300 is provided with (the rank index/thenumber of CWs) S/P (serial parallel conversion) sections betweenmodulation section 208 and multiplexing section 209 of terminal 300shown in FIG. 21. The S/P section converts each serially inputted CW toparallel, divides the converted CWs into a plurality of layers ((therank index/the number of CWs) layers), whereby a plurality of CWs aremapped to as many layers as ranks. When the number of CWs, the rankindex and the number of streams are the same, terminal 300 may apply DFTprocessing and division processing to each CW and then map each CW toeach layer.

<Setting Method 2-1>

In the present setting method, setting section 211 divides the SC-FDMAsignal in accordance with a cluster pattern with a smaller number ofclusters (or a wider cluster size) for a higher rank index during MIMOtransmission.

Hereinafter, this will be described more specifically. Here, a case willbe described as shown in FIG. 22 where the rank index (low, medium,high)) is used. Furthermore, suppose the MCS set (coding rate andmodulation level) set in a CW and coding size are fixed.

For a higher rank index, the scheduler of the base station reduces thenumber of clusters (widens the cluster size). To be more specific, thescheduler of the base station determines a cluster pattern that matchesthe number of clusters (high, medium, low) (or, cluster size (narrow,medium, wide)) according to the rank index (low, medium, high) as shownin FIG. 22.

Division section 212 of setting section 211 divides the CW in accordancewith a cluster pattern with a smaller number of clusters (or a widercluster size) for a higher rank index. To be more specific, when therank index is small (the rank index: 2 in FIG. 23A), division section212 divides the CW of each layer (the number of layers: 2 in FIG. 23A)such that the number of clusters increases (four clusters #0 to #3 inFIG. 23A), that is, the cluster size per cluster becomes narrower. Onthe other hand, when the rank index is large (the rank index: 4 in FIG.23B), division section 212 divides the CW of each layer (the number oflayers: 4 in FIG. 23A) such that the number of clusters decreases (twoclusters #0 and #1 in FIG. 23B), that is, the cluster size becomeswider.

As described above, the higher the rank index, that is, the greater theinterference between layers, the lower is the number of discontinuouspoints in a fluctuation of the equalized channel gain in a combinedsignal in each layer as in the case of setting method 1-1 ofEmbodiment 1. That is, since ISI occurring at combining points(discontinuous points) of clusters can be reduced as the rank indexincreases in each layer, ISI per layer can be reduced. That is, sinceISI per layer is reduced as the rank index increases, it is possible toreduce ISI caused by a certain layer with another layer (ISI betweenlayers).

Thus, the present setting method reduces ISI per layer, and can therebyreduce ISI between different layers, and therefore the base stationwhich is the receiving side can improve transmission characteristics ofeach terminal without deteriorating signal separation capacity in thespace domain. Even when the terminal divides the SC-FDMA signal by thenumber of clusters (the number of divisions) corresponding to the rankindex during MIMO transmission, the present setting method can improveuser throughput for each terminal while maintaining the effect ofimproving system throughput by C-SC-FDMA no matter what the rank indexis, as with setting method 1-1 of Embodiment 1.

<Setting Method 2-2>

According to the present setting method, setting section 211 maps aplurality of clusters to frequency resources in accordance with acluster pattern with a narrower cluster spacing for a higher rank indexduring MIMO transmission.

Hereinafter, this will be described more specifically. Here, a case willbe described as shown in FIG. 24 where the rank index (low, medium,high)) is used. Furthermore, as shown in FIG. 25A and FIG. 25B, supposethe number of clusters of a C-SC-FDMA signal is 2. Furthermore, supposethe MCS set (coding rate and modulation level) set in a CW and codingsize are fixed.

The scheduler of the base station narrows the cluster spacing for ahigher rank index. To be more specific, as shown in FIG. 24, the basestation determines a cluster pattern with a cluster spacing (wide,medium, narrow) according to the rank index (low, medium, high).

Mapping section 213 of setting section 211 maps a plurality of clustersmaking up a CW mapped to each layer to a plurality of discontinuousfrequency resources in accordance with a cluster pattern with a narrowercluster spacing for a higher rank index. To be more specific, when therank index is small (the rank index: 2 in FIG. 25A), mapping section 213maps a plurality of clusters mapped to each layer (the number of layers:2 in FIG. 25A) to frequency resources so that the cluster spacingbecomes wider. On the other hand, when the rank index is large (the rankindex: 4 in FIG. 25B), mapping section 213 maps a plurality of clustersmapped to each layer (the number of layers: 4 in FIG. 25A) to frequencyresources so that the cluster spacing becomes narrower.

Thus, the higher the rank index, that is, the greater the interferencebetween layers, the higher is the frequency correlation between aplurality of clusters making up CWs transmitted in each layer as withsetting method 1-2 of Embodiment 1. It is possible to make a fluctuationof the equalized channel gain at combining points (discontinuous points)of a plurality of clusters more moderate for a higher rank index in eachlayer (that is, difference in equalized channel gain can be reduced),and thereby reduce ISI per layer. That is, as with setting method 2-1,ISI per layer is reduced for a higher rank index and it is therebypossible to reduce ISI (ISI between layers) caused by a certain layerwith different layers.

According to the present setting method as with setting method 2-1, thebase station which is the receiving side can improve transmissioncharacteristics of each terminal without deteriorating signal separationcapacity in the space domain. Thus, according to the present settingmethod, even when the terminal maps a plurality of clusters to frequencyresources at a cluster spacing in accordance with the rank index duringMIMO transmission, it is possible, as with setting method 2-1, toimprove user throughput in each terminal while maintaining the effect ofimproving system throughput by C-SC-FDMA no matter what the rank indexis.

<Setting Method 2-3>

According to the present setting method, setting section 211 uses thesame cluster pattern (the number of clusters, cluster size or clusterspacing) for CWs (SC-FDMA signal) mapped to different layers during MIMOtransmission.

Hereinafter, this will be described more specifically. Here, suppose therank index is 2. As shown in FIG. 26A, of two CWs (CW #1 and CW #2), CW#1 is mapped to layer #0 and CW #2 is mapped to layer #1.

The scheduler of the base station determines the same cluster patternfor CWs (CW #1 and CW #2 shown in FIG. 26A) mapped to different layers(layer #0 and layer #1 shown in FIG. 26A) in terminal 300.

Division section 212 of setting section 211 divides CWs mapped todifferent layers by the same number of clusters (or the same clustersize) to generate a plurality of clusters according to the clusterpattern (the number of clusters or cluster size) reported from the basestation. For example, division section 212 divides both CW #1 mapped tolayer #0 and CW #2 mapped to layer #1 into four clusters #0 to #3 asshown in FIG. 26B.

Furthermore, mapping section 213 of setting section 211 maps CWs (aplurality of clusters divided by division section 212) mapped to thedifferent layers to frequency resources with the same cluster spacing inaccordance with a cluster pattern (cluster spacing) reported from thebase station. For example, mapping section 213 maps clusters #0 to #3 ofCW #1 mapped to layer #0 and clusters #0 to #3 of CW #2 mapped to layer#1 to the same frequency resources with the same cluster spacing asshown in FIG. 26B.

Thus, according to the present setting method, terminal 300 uses thesame cluster pattern for CWs (SC-FDMA signal) mapped to differentlayers, which causes statistical characteristics of ISI in the frequencydomain to become substantially the same between layers. That is,substantially the same ISI occurs between different layers. This reducesthe distribution of ISI power between layers and prevents the occurrenceof ISI between layers whereby a layer having high ISI interferes with alayer having small ISI.

According to the present setting method, the base station can furtherimprove transmission characteristics when a signal separation techniquesuch as PIC (Parallel Interference Canceller) is used whereby signalseparation capacity in the space domain is improved as the difference inreceiving quality between layers decreases. According to the presentsetting method, the statistical characteristics of ISI becomesubstantially the same between layers, which reduces the probabilitythat layers in which receiving quality considerably deteriorates willoccur. The base station can improve average reception characteristics ofall layers and thereby further improve error rate (block error rate)characteristics of CWs.

<Setting Method 2-4>

According to the present setting method, setting section 211 uses thesame cluster pattern (the number of clusters, cluster size or clusterspacing) for an SC-FDMA signal in the same CWs mapped to differentlayers during MIMO transmission.

Hereinafter, this will be described more specifically. Here, suppose therank index is 4. As shown in FIG. 27A, of two CWs (CW #1 and CW #2), CW#1 is mapped to two layers of layer #0 and layer #1, and CW #2 is mappedto two layers of layer #2 and layer #3.

The scheduler of the base station determines the same cluster patternfor the SC-FDMA signal in the same CW mapped to different layers (layers#0 to #3 shown in FIG. 27A) in terminal 300. To be more specific, thescheduler determines the same cluster pattern for CW1 mapped to layer #0and layer #1 shown in FIG. 27A and determines the same cluster patternfor CW2 mapped to layer #2 and layer #3 shown in FIG. 27A.

Division section 212 of setting section 211 divides the SC-FDMA signalin the same CW mapped to different layers by the same number of clusters(or the same cluster size) in accordance with a cluster pattern (thenumber of clusters or cluster size) reported from the base station. Forexample, division section 212 of setting section 211 divides CW #1mapped to layer #0 and layer #1 as shown in FIG. 27B into two clusters(cluster #0, cluster #1) in each layer. Likewise, division section 212divides CW #2 mapped to layer #2 and layer #3 as shown in FIG. 27B intofour clusters (clusters #0 to #3) in each layer.

Furthermore, mapping section 213 of setting section 211 maps the SC-FDMAsignal in the same CWs mapped to different layers to frequency resourceswith the same cluster spacing in accordance with a cluster pattern(cluster spacing) reported from the base station. For example, mappingsection 213 maps clusters #0 and #1 of CW #1 mapped to layer #0 andlayer #1 as shown in FIG. 27B to the same frequency resources with thesame cluster spacing. Likewise, mapping section 213 maps clusters #0 to#3 of CW #2 mapped to layer #2 and layer #3 as shown in FIG. 27B to thesame frequency resources with the same cluster spacing.

Thus, according to the present setting method, terminal 300 uses thesame cluster pattern for the SC-FDMA signal in the same CW mapped todifferent layers and thereby causes statistical characteristics of ISIin the frequency domain to be substantially the same between layers forthe same CW. That is, substantially the same ISI occurs in differentlayers to which the same CW is mapped. That is, in different layers towhich the same CW is mapped, the magnitude of ISI generated per layerand ISI between layers are substantially the same. Thus, the magnitudeof ISI becomes uniform in the same CW.

According to the present setting method, since the difference inreceiving quality between layers can be reduced for the same CW, it ispossible to improve coding gains for coding and improve receptioncharacteristics. That is, according to the present setting method, it ispossible to make the distribution of ISI received by each bit (or eachsymbol) in the same CW substantially uniform, that is, suppress thedistribution of LLR (Log Likelihood Ratio) per bit (or symbol) in CW toa small level. This makes it possible to improve receptioncharacteristics for each CW.

<Setting Method 2-5>

According to the present setting method, of CWs (SC-FDMA signal) mappedto different layers during MIMO transmission, setting section 211decreases the number of clusters (or widens the cluster size) for CWs(SC-FDMA signal) having a higher transmission rate (MCS set).

Hereinafter, this will be described more specifically. Here, terminal300 applies coding processing and modulation processing to CWs usingdifferent MCS sets for the respective CWs, performs link adaptation inthe space domain, and thereby transmit a plurality of CWs havingdifferent transmission rates in parallel in the space domain. Forexample, a case as shown in FIG. 28 will be described where atransmission rate (MCS set) (low, medium, high) is used. A high MCS set(coding rate: high, modulation level: high) is set in CW #1 and a lowMCS set (coding rate: low, modulation level: low) is set in CW #2 shownin FIG. 29. Furthermore, CW #1 is mapped to layer #0 and CW #2 is mappedto layer #1.

Of a plurality of CWs mapped to different layers and transmitted byterminal 300, the scheduler of the base station determines a clusterpattern having a smaller number of clusters (wider cluster size) for CWshaving a higher transmission rate (MCS set). To be more specific, asshown in FIG. 28, the base station determines a cluster pattern thatmatches the number of clusters (high, medium, low) (or cluster size(narrow, medium, wide)) according to the MCS set (low, medium, high).

Of the plurality of CWs mapped to different layers, setting section 211decreases the number of clusters (widens the cluster size) for CWs of ahigher MCS set. To be more specific, setting section 211 decreases thenumber of clusters for CW #1 having a higher MCS set as shown in FIG. 29(two clusters #0 and #1 in FIG. 29), that is, widens the cluster sizeper cluster. On the other hand, setting section 211 increases the numberof clusters for CW #2 having a lower MCS set (four clusters #0 to #3 inFIG. 29), that is, narrows the cluster size per cluster.

Thus, for CWs having a higher transmission rate (MCS set), that is, CWsmore susceptible to the influence of ISI (CWs having lower allowableISI), the number of discontinuous points in a fluctuation of theequalized channel gain of a combined signal decreases as with settingmethod 1-1 of Embodiment 1. It is thereby possible to reduce ISIoccurring at combining points (discontinuous points) in a plurality ofclusters for CWs having a higher transmission rate (MCS set).

Furthermore, setting section 211 increases the number of clusters(narrows the cluster size) for CWs having a lower transmission rate (MCSset), that is, CWs less susceptible to the influence of ISI (CWs havinggreater allowable ISI). This increases the number of discontinuouspoints in a fluctuation of the equalized channel gain in a combinedsignal as with setting method 1-1 of Embodiment 1 in the base station,but since robustness against ISI is high, it is possible to improve thefrequency diversity effect in the range of allowable ISI.

Thus, the present setting method sets the number of clusters (clustersize) for CWs of different transmission rates (MCS sets), and canthereby improve throughput per CW. That is, overall throughput (userthroughput) of a plurality of CWs can be improved as a consequence.

<Setting Method 2-6>

According to the present setting method, of CWs (SC-FDMA signal) mappedto different layers during MIMO transmission, setting section 211narrows a cluster spacing for CWs (SC-FDMA signal) having a highertransmission rate (MCS set).

Hereinafter, this will be described more specifically. Here, as withsetting method 2-5, terminal 300 performs link adaptation in the spacedomain using different MCS sets for respective CWs. A case will bedescribed as an example where a transmission rate (MCS set) (low,medium, high) is used as shown in FIG. 30. Furthermore, as with settingmethod 2-5, a high MCS set (coding rate: high, modulation level: high)is set in CW #1 shown in FIG. 31 and a low MCS set (coding rate: low,modulation level: low) is set in CW #2. Furthermore, CW #1 is mapped tolayer #0 and CW #2 is mapped to layer #1.

Of a plurality of CWs mapped to different layers and transmitted byterminal 300, the scheduler of the base station determines a clusterpattern with a narrower cluster spacing for CWs having a highertransmission rate (MCS set). To be more specific, as shown in FIG. 30,the base station determines a cluster pattern with a cluster spacing(wide, medium, narrow) according to the MCS set (low, medium, high).

Of the plurality of CWs mapped to different layers, setting section 211narrows the cluster spacing for CWs having a higher MCS set. To be morespecific, setting section 211 narrows the cluster spacing for CW #1having a higher MCS set as shown in FIG. 31. On the other hand, settingsection 211 widens the cluster spacing for CW #2 having a lower MCS set.

Thus, for CWs having a higher transmission rate (MCS set), that is, forCWs more susceptible to the influence of ISI (CWs having lower allowableISI), the frequency correlation among a plurality of clusters making upa CW is increased as with setting method 1-2 of Embodiment 1. This makesit possible to make more moderate a fluctuation of the equalized channelgain at combining points (discontinuous points) of a plurality ofclusters for CWs having a higher transmission rate (MCS set) (that is,the difference in equalized channel gain can be reduced), and therebyreduce ISI in a CW.

Furthermore, setting section 211 widens the cluster spacing for CWshaving a lower transmission rate (MCS set), that is, for CWs lesssusceptible to the influence of ISI (CWs having greater allowable ISI).Although this makes the fluctuation of the equalized channel gain atcombining points (discontinuous points) of the combined signal moreabrupt (that is, the difference in equalized channel gain increases) aswith setting method 1-2 of Embodiment 1, the base station can improvethe frequency diversity effect in the range of allowable ISI becauserobustness against ISI is sufficiently high.

Thus, the present setting method sets the cluster spacing according toCWs having different transmission rates (MCS sets), and can therebyimprove throughput per CW as with setting method 2-5. That is, it ispossible to improve overall throughput (user throughput) of a pluralityof CWs as a consequence.

Setting methods 2-1 to 2-6 have been described so far.

Thus, the present embodiment can obtain effects similar to those inEmbodiment 1 even when MIMO transmission is used.

In the present embodiment, the base station may also set a threshold ofthe rank index to determine a cluster pattern in the same way as inEmbodiment 1 (FIG. 16A to FIG. 19C). Hereinafter, an example where thebase station sets a threshold and determines a cluster pattern will bedescribed using FIGS. 32A to 32E. In FIGS. 32A to 32E, B_(i) (i=0, 1, .. . ) is a bandwidth (cluster size) per cluster and indicates, forexample, a minimum bandwidth (minimum cluster size) defined for everyrange separated by a threshold and holds the relationshipB_(i)≦B′_(i+1). Furthermore, B′_(i) (i=0, 1, . . . ) represents amaximum cluster spacing defined for every range separated by a thresholdand holds the relationship B′_(i)≧B′_(i+1).

For example, as shown in FIG. 32A, the base station may also set athreshold for each rank index, compare the rank index (RI) of eachterminal with the threshold and determine the number of clusters (X). Tobe more specific, the base station determines the number of clusters Xto be 4 when the rank index RI is 1 and determines the number ofclusters X to be 3 when the rank index RI is 2. The same applies to acase where the rank index RI is 3 or 4. That is, in FIG. 32A, a fixednumber of clusters is set for the rank index.

Furthermore, as shown in method 1 in FIG. 32B, the base station may seta threshold for each rank index and set an upper limit of the number ofclusters X for each rank index. For example, as shown in method 1 ofFIG. 32B, the base station determines one number of clusters whose upperlimit is the number of clusters X=4 when the rank index RI is 1 anddetermines one number of clusters whose upper limit is the number ofclusters X=3 when the rank index RI is 2. The same applies to a casewhere the rank index is 3 or 4. Setting section 211 of each terminalsets the number of clusters according to the rank index in this way, andcan thereby limit the maximum value of ISI per layer so as to preventISI from a different layer from exceeding allowable ISI. Thus, the basestation can correctly select an MCS set of each layer in each terminal.Furthermore, as shown in method 2 in FIG. 32B, the base station may alsoset a lower limit and an upper limit of the number of clusters for eachrank index. For example, as shown in method 2 in FIG. 32B, the basestation determines one number of clusters in a range of 2≦X≦4 when therank index RI is 1 and determines one number of clusters in a range of2≦X≦3 when the rank index RI is 2. As shown in FIG. 3A or FIG. 3B, thisallows the setting section 211 of each terminal to set only such anumber of clusters X that matches the user throughput of a certain valueor above including the maximum value. Furthermore, the base station canreduce the number of reporting bits to report the number of clusters Xper layer.

Furthermore, as shown in FIG. 32C, the base station may also set athreshold so as to separate between a plurality of rank indexes forevery certain range of rank index and set a cluster size (Y) for everyrange of rank index. According to method 1 in FIG. 32C, as with method 1in FIG. 32B, the base station determines one cluster size Y whose lowerlimit is a minimum cluster size (B₀, B₁, B₂, B₃ shown in method 1 inFIG. 32C) defined for every range of rank index. As shown in method 1 inFIG. 32C, when the rank index RI is 1 to 2 which is a range having thelowest rank index (that is, allowable ISI is maximum), the base stationmay arbitrarily set cluster size Y. Furthermore, according to method 2in FIG. 32C, as with method 2 in FIG. 32B, an upper limit and a lowerlimit of the cluster size are set for every range of rank index.

Furthermore, when the base station calculates cluster size (Y) using thenumber of clusters (X), as shown in FIG. 32D, the base station may set athreshold for each rank index, set the number of clusters X_(ri) foreach rank index and calculate cluster size Y. Here, X_(ri) (ri=0, 1, 2,. . . , ri is a number assigned for every range of the rank indexseparated by a threshold) represents the number of clusters set for eachrank index in each range (ri). Furthermore, B represents the totalbandwidth (that is, the sum of cluster sizes) used for a C-SC-FDMAsignal. To be more specific, in FIG. 32D, the base station calculatescluster size Y=B/X_(ri) set in the rank index using the number ofclusters X_(ri) set for each rank index (ri=0, 1, 2, . . . ).

Furthermore, as shown in FIG. 32E, the base station may also set clusterspacing (Z) for each rank index by setting a threshold for each rankindex. In FIG. 32E, the base station determines cluster spacing Z whoseupper limit corresponds to a maximum cluster spacing (B′₀, B′₁, B′₂, B′₃shown in FIG. 32E) for each rank index. As shown in FIG. 32E, when therank index RI is 1, the base station may set an arbitrary value forcluster spacing Z.

A case has been described in the present embodiment in FIG. 23B, FIG.25B and FIG. 27A where the S/P section in terminal 300 converts CW fromserial to parallel and the DFT section performs DFT processing. However,in terminal 300 of the present invention, the DFT section may performDFT processing on a CW and then the S/P section may convert the CW fromserial to parallel as shown in FIG. 23B, FIG. 25B and FIG. 27A.

Furthermore, the present embodiment is applicable to both single user(SU)-MIMO transmission (that is, MIMO transmission between a pluralityof antennas of one base station and a plurality of antennas of oneterminal) and multiuser (MU)-MIMO transmission (that is, MIMOtransmission between a plurality of antennas of one base station and aplurality of antennas of a plurality of terminals).

Furthermore, a case has been described with setting methods 2-1 and 2-2of the present embodiment where a cluster pattern is determinedaccording to the rank index. However, the present invention candetermine a cluster pattern according to the number of spatiallymultiplexed CWs. This makes it possible to control the magnitude of ISIbetween different CWs according to the number of CWs and improvetransmission characteristics per CW. This increases the probability ofbeing able to select an MCS set with higher efficiency of use offrequency resources, and can thereby further improve user throughput.

Furthermore, MIMO transmission using precoding has been described in thepresent embodiment, but the present invention is also applicable to MIMOtransmission without precoding (that is, when a precoding matrix isassumed as a unit matrix).

The embodiments of the present invention have been described so far.

A case has been described in the above embodiments where a clusterpattern is controlled according to an MCS set, coding size or rankindex. However, as the number of frequency resources allocated to asignal transmitted by the terminal, the number of resource elements (RE)or the number of RBs bundling a plurality of REs decreases, the presentinvention may reduce the number of clusters (widen the cluster size) ornarrow the cluster spacing. This allows effects similar to those in theabove embodiments to be thereby obtained.

Furthermore, the present invention may combine Embodiment 1 andEmbodiment 2.

Furthermore, the terminal may also be called “UE (User Equipment)” andthe base station may also be called “Node B or BS (Base Station).”

Moreover, although cases have been described with the embodiments abovewhere the present invention is configured by hardware, the presentinvention may be implemented by software.

Each function block employed in the description of the aforementionedembodiment may typically be implemented as an LSI constituted by anintegrated circuit. These may be individual chips or partially ortotally contained on a single chip. “LSI” is adopted here but this mayalso be referred to as “IC,” “system LSI,” “super LSI” or “ultra LSI”depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells within an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosure of Japanese Patent Application No. 2008-292653, filed onNov. 14, 2008, including the specification, drawings and abstract isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a mobile communication system orthe like.

1. A communication apparatus, comprising: a scheduler, which, inoperation, determines a resource allocation to map each of a pluralityof precoded symbol sequences to a plurality of frequency resources, eachof the plurality of frequency resources being located on a separateposition from other frequency resource(s) on a frequency axis, whereinthe plurality of precoded symbol sequences are to be generated bymultiplying a plurality of symbol sequences by a precoding matrix, eachsymbol sequence corresponding to one of a plurality of layers, wherein afirst plurality of frequency resources to which a first precoded symbolsequence is mapped, and a second plurality of frequency resources towhich a second precoded symbol sequence is mapped share: a number ofclusters used to map each precoded symbol sequence; cluster sizes; and afrequency position of each cluster, each of the cluster sizes being adiscontinuous frequency bandwidth; a transmitter, which, in operation,transmits information indicating the determined resource allocation; areceiver, which, in operation, receives a signal including the pluralityof precoded symbol sequences which are mapped to the plurality offrequency resources; and a combiner, which, in operation, combines theplurality of frequency resources to generate symbol sequences.
 2. Thecommunication apparatus according to claim 1 wherein a cluster size isequal to or larger than a minimum cluster size which is common among theplurality of layers.
 3. The communication apparatus according to claim 1wherein a rank index indicating a number of layers is equal to or lessthan a number of antennas associated with the received signal.
 4. Thecommunication apparatus according to claim 1 wherein each of theplurality of precoded symbol sequences is a symbol sequencecorresponding to different codeword from that for other precoded symbolsequences.
 5. The communication apparatus according to claim 5 wherein anumber of layers is equal to a number of codewords.
 6. The communicationapparatus according to claim 1 wherein when a number of codewords issmaller than a number of layers, the plurality of precoded symbolsequences derive from a plurality of symbol sequences corresponding to asame codeword.
 7. The communication apparatus according to claim 1wherein when a plurality of codewords are used, the plurality ofprecoded symbol sequences derive from a plurality of first symbolsequences corresponding to a first codeword and a plurality of secondsymbol sequences corresponding to a second codeword which is differentfrom the first codeword.
 8. The communication apparatus according toclaim 7 wherein a number of layers corresponding to the first codewordis equal to a number of layers corresponding to the second codeword. 9.A resource allocation method, comprising: determining a resourceallocation to map each of a plurality of precoded symbol sequences to aplurality of frequency resources, each of the plurality of frequencyresources being located on a separate position from other frequencyresource(s) on a frequency axis, wherein the plurality of precodedsymbol sequences are to be generated by multiplying a plurality ofsymbol sequences by a precoding matrix, each symbol sequencecorresponding to one of a plurality of layers, wherein a first pluralityof frequency resources to which a first precoded symbol sequence ismapped, and a second plurality of frequency resources to which a secondprecoded symbol sequence is mapped share: a number of clusters used tomap each precoded symbol sequence; cluster sizes; and a frequencyposition of each cluster, each of the cluster sizes being adiscontinuous frequency resource bandwidth; transmitting informationindicating the determined resource allocation; and receiving a signalincluding the plurality of precoded symbol sequences which are mapped tothe plurality of frequency resources; and combining the plurality offrequency resources to generate symbol sequences.
 10. The resourceallocation method according to claim 9 wherein a cluster size is equalto or larger than a minimum cluster size which is common among theplurality of layers.
 11. The resource allocation method according toclaim 9 wherein a rank index indicating a number of layers is equal toor less than a number of antennas associated with the received signal.12. The resource allocation method according to claim 9 wherein each ofthe plurality of precoded symbol sequences is a symbol sequencecorresponding to different codeword from that for other precoded symbolsequences.
 13. The resource allocation method according to claim 12wherein a number of layers is equal to a number of codewords.
 14. Theresource allocation method according to claim 9 wherein when a number ofcodewords is smaller than a number of layers, the plurality of precodedsymbol sequences derive from a plurality of symbol sequencescorresponding to a same codeword.
 15. The resource allocation methodaccording to claim 9 wherein when a plurality of codewords are used, theplurality of precoded symbol sequences derive from a plurality of firstsymbol sequences corresponding to a first codeword and a plurality ofsecond symbol sequences corresponding to a second codeword which isdifferent from the first codeword.
 16. The resource allocation methodaccording to claim 15 wherein a number of layers corresponding to thefirst codeword is equal to a number of layers corresponding to thesecond codeword.